As someone who tends towards (lowercase "l", as in not literally the party of that name) libertarian-ism (I prefer classical liberalism label, but that just confuses most people) and despises the two-party system, I tend to say that people like Milo are simply opportunists who have warped true libertarian ideals into a internet flame war. He plays to a few legitimate issues, then twists them up in order to build his support. (Which is the case for every political commentator or politician, ever.)
Going back to the the original progressive movements in the late 1800s and early 1900s, there was a strong need for much of the work that was done. This continued through the 1900s, the civil rights eras, and so forth. The armchair political scientist that I am, I believe the problem we see today really took hold though when progressive ideologies failed to do some basic rebranding. Viktor hit the nail on the head with what he said about Feminism as a prime example. The name alone is a big part of the problem, feminism, as it makes people think not of equal rights (the most mainstream definition of modern feminism), but of additional rights for women specifically as it outright has the fem- prefix at all. And in politics, it doesn't matter what is true or not, what matters is the perception. And the perception isn't great. When combined with the usual radicals, political correctness, and youtube SJWs (who are often massive hypocrites), this just created the breeding ground for a backlash that fed the growth of the alt-right. Well, Milo and his ilk saw this, and instead of trying to moderate the tone of the radicals on both sides, just played to the other side of the radical equation with an audience that liked the fact they could say "We're not homophobic, one of our spokesmen is gay!"
Of course, meanwhile the Milos on the progressive side do the same thing, and playing to their own base they in turn play into the talking points of the alt-right Milos creating a feedback loop that never ends. The clearest example goes back to the feminism issue, with the women make 78% of what men make statistic. The problem being that while an income (not technically wage) gap definitely exists, it does not translate into women making 78% of what men do for the exact same work, at the exact same hours, at the exact same job. (Instead that number hinges a lot on issues such as imbalances in women in high paying positions such as corporate executives, jobs with hazard pay, women working less hours, and so forth, and was never intended to be a statement of less pay for equal work.) So the Milos take this simple truth, twist it back around into an attack on men, which riles his base. The riled up men come across as sexist idiots for daring to say no to equal pay (which is a terrible thing to look like you're saying no to), creating even more misperception, more talking points for the other side, and so on and so on ping ponging back and forth until no one says an ounce of truth at all anymore because their responses are falsehoods in response to a falsehood which itself was in response to a falsehood.
That's why I voted for Jimmy McMillan, he's a karate master and will lower the rent. (Just to be clear, this was a joke. I absolutely did not vote for the crazy man no matter how awesome he is.

) Mostly I'm just bored during hurricane downtime and wanted to hear myself talk. Or... well... read myself type?
Addendum: I should clarify my point, I went off on a bit of a tangent I think. Basically, I'm just saying be careful not to dismiss a few of the root issues that may actually be valid, even if they are championed by a madman. The key is to address the valid points from all sides of an argument while filtering out the noise. Easier said than done, of course. Milo is a terrible messenger, but he isn't 100% wrong. Just... you know, 98% wrong. The best way to deal with anyone like that though is address the 2% in a thoughtful manner, and suddenly the 98% has no leg to stand on.