Paul certainly was not saying that for a morally clean Christian, absolutely everything is clean and permissible.
لَاحِظِ ٱلتَّبَايُنَ ٱلْمَوْجُودَ فِي هذِهِ ٱلْآيَةِ :‏ « كُلُّ ٱلْأَشْيَاءِ طَاهِرَةٌ لِلطَّاهِرِينَ .‏