I don't trust humanity yet, and maybe it will never happen. But I know it's possible, and what's more important--it's the right thing. And that alone makes it worth pursuing.
No ancap person I'm aware of sees it as a utopia. They won't promise 'a chicken will fly into your mouth and the rivers will run with lemonade' as the communists did. There will still be violence, drug use, and prostitution, but the difference is that it won't be inherent, sanctioned, and systematic as it is with the state. We can all agree that at least on most things, the situation is better when the government stays out of it and free markets and peaceful cooperation are allowed to flourish. Of course I believe that system to be better, or else I wouldn't be advocating for it. But I'm allowed to strive for improvement without being a utopian.
The other thing about ancap is that pieces of it have been tried successfully around the world in the past and present, so it's analogous to building a new machine where all the separate components already exist. Facets x, y, an z have been tried or are currently being implemented around the world. Sometimes a society just did x, sometimes just y, and one time another society did x and y, while another did y an z, etc. There are no laws of physics or math or economics or human behavior that prohibit doing x, y, and z. But there's no doubt it's a long shot. Some human beings really, really enjoy robbing and murdering eachother, and they always seem to end up tricking people into giving them power. But a certain percentage of people must learn to refuse to sanction violence. Not everyone needs to understand Austrian economics for ancap to flourish, just as only 1/3 of Americans supported the revolution, and probably only a fraction of them understood it. A handful will always be against an idea, a handful will be for it, and the big lump in the middle of the bell curve just wants to eat Mac n cheese and watch honey booboo.
Tu ne cede malis sed contra audentior ito