Conscientious objector
The Book of Discipline of the Reformed Free Methodist Church teaches:

Militarism is contrary to the spirit of the New Testament and the teachings of Jesus Christ. Even from humanitarian principles alone, it is utterly indefensible. It is our profound and God-given conviction that none of our people be required to participate in war of any form and that these God-given convictions of our members be respected.
Since the American Civil War, Seventh-day Adventists have been known as non-combatants, and have done work in hospitals or to give medical care rather than combat roles, and the church has upheld the non-combative position. Jehovah's Witnesses and Christadelphians, refuse to participate in the armed services on the grounds that they believe they should be neutral in worldly conflicts and often cite the latter portion of Isaiah 2:4 which states, "...neither shall they learn war anymore". Other objections can stem from a deep sense of responsibility toward humanity as a whole, or from simple denial that any government possesses the moral authority to command warlike behavior from its citizens.
The varied experiences of non-combatants are illustrated by those of Seventh-day Adventists when there was mandatory military service: "Many Seventh-day Adventists refuse to enter the army as combatants, but participate as medics, ambulance drivers, etc. During World War II in Germany, many SDA conscientious objectors were sent to concentration camps or mental institutions; some were executed. Some Seventh-day Adventists volunteered for the US Army's Operation Whitecoat, participating in research to help others. The Church preferred to call them "conscientious participants", because they were willing to risk their lives as test subjects in potentially life-threatening research. Over 2,200 Seventh-day Adventists volunteered in experiments involving various infectious agents during the 1950s through the 1970s in Fort Detrick, MD." Earlier, a schism arose during and after World War I between Seventh-day Adventists in Germany who agreed to serve in the military if conscripted and those who rejected all participation in warfare—the latter group eventually forming a separate church (the Seventh Day Adventist Reform Movement).

In the early Christian Church followers of Christ refused to take up arms.

In as much as they [Jesus' teachings] ruled out as illicit all use of violence and injury against others, clearly implied [was] the illegitimacy of participation in war ... The early Christians took Jesus at his word, and understood his inculcations of gentleness and non-resistance in their literal sense. They closely identified their religion with peace; they strongly condemned war for the bloodshed which it involved.
After the Roman Empire officially embraced Christianity, the just war theory was developed in order to reconcile warfare with Christian belief. After Theodosius I made Christianity an official religion of the Empire, this position slowly developed into the official position of the Western Church. In the 11th century, there was a further shift of opinion in the Latin-Christian tradition with the crusades, strengthening the idea and acceptability of holy war. Objectors became a minority. Some theologians see the Constantinian shift and the loss of Christian pacifism as the great failing of the Church.
Ben Salmon was a Catholic conscientious objector during World War I and outspoken critic of Just War theology. The Catholic Church denounced him and The New York Times described him as a "spy suspect". The US military (in which he was never inducted) charged him with desertion and spreading propaganda, then sentenced him to death (this was later revised to 25 years hard labor). On June 5, 1917, Salmon wrote in a letter to President Wilson:

Regardless of nationality, all men are brothers. God is "our Father who art in heaven". The commandment "Thou shalt not kill" is unconditional and inexorable. ... The lowly Nazarene taught us the doctrine of non-resistance, and so convinced was he of the soundness of that doctrine that he sealed his belief with death on the cross. When human law conflicts with Divine law, my duty is clear. Conscience, my infallible guide, impels me to tell you that prison, death, or both, are infinitely preferable to joining any branch of the Army.
Nowadays, the Catholic Church teaches that "Public authorities should make equitable provision for those who for reasons of conscience refuse to bear arms; these are nonetheless obliged to serve the human community in some other way." (point 2311 of the Catechism of the Catholic Church)
Because of their conscientious objection to participation in military service, whether armed or unarmed, Jehovah's Witnesses have often faced imprisonment or other penalties. In Greece, for example, before the introduction of alternative civilian service in 1997, hundreds of Witnesses were imprisoned, some for three years or even more for their refusal. In Armenia, young Jehovah's Witnesses were imprisoned because of their conscientious objection to military service; this was discontinued in November 2013. The government of South Korea also imprisons hundreds for refusing the draft. In Switzerland, virtually every Jehovah's Witness is exempted from military service.
For believers in Indian religions, the opposition to warfare may be based on either the general idea of ahimsa, nonviolence, or on an explicit prohibition of violence by their religion, e.g., for a Buddhist, one of the five precepts is "Pānātipātā veramaṇi sikkhāpadam samādiyāmi", or "I undertake the precept to refrain from destroying living creatures", which is in obvious opposition to the practice of warfare. The 14th Dalai Lama has stated that war "should be relegated to the dustbin of history". On the other hand, many Buddhist sects, especially in Japan, have been thoroughly militarized, warrior monks (yamabushi or sōhei) participating in the civil wars. Hindu beliefs do not go against the concept of war, as seen in the Gita. Both Sikhs and Hindus believe war should be a last resort and should be fought to sustain life and morality in society.
Followers of the Baháʼí Faith are advised to do social service instead of active army service, but when this is not possible because of obligations in certain countries, the Baháʼí laws include loyalty to one's government, and the individual should perform the army service.
Some practitioners of pagan religions, particularly Wicca, may object on the grounds of the Wiccan rede, which states "An it harm none, do what ye will" (or variations). The threefold law may also be grounds for objection.
A notable example of a conscientious objector was the Austrian devout Roman Catholic Christian Franz Jägerstätter, who was executed on August 9, 1943, for openly refusing to serve in the Nazi Wehrmacht, consciously accepting the penalty of death. He was declared Blessed by Pope Benedict XVI in 2007 for dying for his beliefs, and is viewed as a symbol of self-sacrificing resistance.

Alternatives for objectors: Some conscientious objectors are unwilling to serve the military in any capacity, while others accept noncombatant roles. While conscientious objection is usually the refusal to collaborate with military organizations, as a combatant in war or in any supportive role, some advocate compromising forms of conscientious objection. One compromising form is to accept non-combatant roles during conscription or military service. Alternatives to military or civilian service include serving an imprisonment or other punishment for refusing conscription, falsely claiming unfitness for duty by feigning an allergy or a heart condition, delaying conscription until the maximum drafting age, or seeking refuge in a country which does not extradite those wanted for military conscription. Avoiding military service is sometimes labeled draft dodging, particularly if the goal is accomplished through dishonesty or evasive maneuvers. However, many people who support conscription will distinguish between "bona fide" conscientious objection and draft dodging, which they view as evasion of military service without a valid excuse.
Conservative Mennonites do not object to serving their country in peaceful alternatives (alternative service) such as hospital work, farming, forestry, road construction and similar occupations. Their objection is in being part in any military capacity whether noncombatant or regular service. During World War II and the Korean, Vietnam war eras they served in many such capacities in alternative I-W service programs initially through the Mennonite Central Committee and now through their own alternatives.
Despite the fact that international institutions such as the United Nations (UN) and the Council of Europe (CoE) regard and promote conscientious objection as a human right, as of 2004, it still does not have a legal basis in most countries. Among the roughly one-hundred countries that have conscription, only thirty countries have some legal provisions, 25 of them in Europe. In Europe, most countries with conscription more or less fulfill international guidelines on conscientious objection legislation (except for Greece, Cyprus, Turkey, Finland and Russia) today. In many countries outside Europe, especially in armed conflict areas (e.g. Democratic Republic of the Congo), conscientious objection is punished severely.
In 1991, The Peace Abbey established the National Registry for Conscientious Objection where people can publicly state their refusal to participate in armed conflict.

Informed Consent Violations: In some cases, conscientious objectors have been interned in concentration-camp-like conditions, which would be coercive for objectors to "volunteer" for quasi-ethical experimentation.