So, when I describe myself as a Marxist, I am usually explicit about endorsing Marx's critique of capitalism - but not his notion of history, particularly the part about the socialist utopia. I can say more about the critique of capitalism at some point, but I want to focus on the second half. I will try to clarify this point by saying that Marx didn't have a good understanding of human nature: people tend to be horrible to one another.
So far, so good. But I hadn't remembered putting this in terms of Hobbes versus Rousseau before. Hobbes (very roughly speaking) thinks that people are basically bad, and that society has a good influence, keeping our aggression in check. Rousseau (again, very roughly) sees people as basically good, and society as inherently corrupting. (I know that is a cartoonish view of their position, and look! You get actual cartoons as well!) To connect these pieces: Marx follows Rousseau, but the so-called Communist states tend to get pretty Hobbesian (arguably, Marx's theory has never been put into practice, but I'm not sure what it would take to implement it well, and of course his view of history said that this would arise naturally in any case, which obviously hasn't happened).
What's the converse of this? I tend to see libertarians as the opposite - and the (new insight) that struck me is that the libertarians I've talked to tend to endorse a Rousseau-esque view of human nature. It goes something like this: "If only we got rid of all the regulation, people would just naturally behave, rather than spending so much time trying to conform to, or subvert, unnecessary rules." Maybe you would phrase this differently, but this seems to be the gist as I understand it, from talking with several different libertarians over the years.
And what's wrong with this? Well, it's either very naive - I mean, seriously, do they understand that the regulations tend to be in response to people doing bad things in the first place? - or else extremely cynical. I'm willing to give the libertarians I know the benefit of the doubt, but it does seem in general that there's a cynicism to libertarians in general that I really, really dislike.
That said, I'll say one thing for Ayn Rand: at least she's honest about being an unapologetic asshole.