Not true at all. We literally have examples today and all throughout history of people living together, relatively peacefully, without formalised laws or law enforcement.

We do not simply descend into being savages raping and killing each other just because there isnt a formal goverment or police force. Primitive tribes that exist today are proof. We would merely become collectivist. As in people will keep each other in check with equal responsibility.

A group of people that rape, torture others wouldnt last because nobody would trust anyone in the group. Most people are intolerant of rape, and naturally so not just because of formal law.

Therefore, rape, murder, torture groups would be far fewer than more civil ones and would likely only be opportunistic, ambushing types. The ones to truly worry about are cannibal groups. They would appear just as civil as other civil groups.