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 a group of people whose job is to exploit and victimize us are most likely beyond reasoning with, but as with many untrue ideas, there are numerous ways to show how it's false, and the premise of this argument itself is one that I feel doesn't get enough attention. I want to point out just a few of the outstanding examples of non-enforced human altruism that are so powerful and undeniable that they are 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 how Wikipedia is a leftist propaganda platform, but that doesn't change the fact that when they're not talking about politics or philosophy their information is usually good and it doesn't change the fact that the people who write that stuff are not usually getting personally rewarded.
Soldiers. Perhaps the strongest example: there are so many people willing to risk their lives to do what they believe protects other people (albeit it's not actually helping in most cases but that's not the soldiers' fault) that the US government can get enough people to fight their wars without forcing anyone into service. And yes I know soldiers get paid but I don't think self-interest alone accounts for their actions, given how much easier it probably is to make a better living on a safer occupation working in the market.
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? It'd be the opposite since government is by the far the largest committer of violent crimes per capita, including armed extortion and kidnapping of innocents. Most Anarchists argue for a society where crime-fighting and protection services are provided on a free-market basis involving voluntary assocation and the option to opt out, but even besides how obviously better that is, a quick glance at the real world makes it abundantly clear that there would be people willing to do it for free for those who really couldn't afford it.