Many arguments against anarchism are based on the platitude that people are selfish and that without a government to force them to behave ethically they'll inevitably exploit and victimize each other to no end.
Obviously the people who use this idea to justify said selfish people picking a group of them to be granted the arbitrary authority to define what actions are acceptable are most likely beyond reasoning with, but as with most arguments against anarchism, there's more than one problem with it, and I feel the premise of this argument doesn't get enough attention. Let me point out just a few of the outstanding examples of non-enforced human altruism that are big enough to be a major part of many of our lives.
Open-source software, most notably Unix and everything surrounding it. Thousands if not millions of people put enormous time and effort into making this software for anyone and everyone to benefit from and they're not making money from it.
Q&A sites like Stack Exchange and Quora, where thousands if not millions of people repeatedly answer other people's questions and help them solve their problems for no personal gain. Also mailing lists in the Unix community are a popular place for this type of beautiful interaction, though you won't know see that much if you're not involved in the Unix community.
Wikipedia. How many people have devoted massive quantities of their time to giving other people information for free?
I've written at length about Wikipedia's liberal bias, but outside of politics or philosophy their information is usually good, and the people who write that stuff are not usually getting personally rewarded.
If people do all these things as volunteers, just how stupid do you have to be to think that without the government society would devolve into chaos and violence everywhere?