I'm not a libertarian any more. I was never that hardcore of one, in that I stuck with libertarian policies mainly because I found them practical. Further research has revealed that some of them aren't that practical, so I abandoned them. Libertarianism doesn't reliably care for the poor, protect the environment, or prevent massive corporations from taking advantage of ordinary people. That stuff is important enough to be a dealbreaker.
But of course, when you suggest that complete anarcho-capitalism isn't ideal, people demand to know whether you're a socialist. Trouble is, socialism seems to have shifting definitions. Is the gold standard for socialism the USSR, or Norway, or maybe Venezuela? If you propose a single change, like universal healthcare, you're told that's socialist. But that one policy certainly doesn't make a country equivalent to China or Cuba. There are a lot of stops on a scale from pure anarchy to pure communism - both of which, proponents will tell you, have never actually existed in real life, not on a large scale.
And one of those stops is the US. The US is not libertarian or purely capitalist. We have socialized education, socialized libraries, and a socialized retirement program. The government manages labor laws, breaks up monopolies, and injects cash into the economy to stave off recessions. Whether it's successful at any of those is always a matter for debate.
I read a book some years ago about North Korea. The North Korean defectors spotlighted in the book knew their communist system had flaws, but they were sure it was better than the alternative, which they imagined was something out of a Dickens novel. Child labor, grinding poverty with no aid available, no free schools, no affording a doctor if you're poor. What convinced them communism wasn't actually the best option was learning Western nations had modified their capitalist systems so they weren't like that anymore.
Which of course is exactly what happened. America isn't purely capitalist because we tried that and it was bad, so we established some safety nets and that was better. Capitalism isn't ruined just because there's an income tax or some food stamps.
So how much government intervention do you have to have before it's socialism? Frankly, I don't know and don't care; that's a question on the order of "is taxation theft," namely, arguing about definitions rather than realities. The real question is, how much management of the economy, in the form of graduated tax brackets and social programs, would it take to remove the advantages of having a free economy?
The advantages of a free economy include flexibility (there are lots of kinds of jobs and products, new products can arise all the time, prices are responsive to demand) and the ability to affect your own situation by working. Decentralizing decision-making means one person making a stupid decision won't cause an entire industry to go under. Income tax doesn't change these things significantly, not unless it's many times higher than what we have. Some socialist policies do threaten them. For instance, subsidizing anything risks increasing its price uncontrollably- since people aren't paying directly, they won't stop purchasing even if the price gets exorbitant (see: higher education, houses, healthcare*).
[*though with healthcare, since we need it to live, it's never going to be perfectly price-controlled by demand.]
So we just have to be careful with it. The main thing I learned when I was studying the food system is that there are no simple solutions. Some horrible situations (like, for instance, e. coli in meat, or small farms going under) are caused by too little regulation, others by too much. Sometimes it's just the wrong regulation, either because lobbyists got through something to protect their interests, or because people didn't think through the consequences of their actions. So, whether we're adding regulations or taking them away, we have to be smart about it. That's a lot more important than whether something is "socialist" or not. We also have to consider who the policy will benefit: the ones in our society who need it most, or the ones who are doing fine and will continue to?
My current favorite candidate is Elizabeth Warren. She is concerned with helping those who need it most, and just as important, she's run the numbers and actually has a plan for everything. She's practical, and I like that.
Don't get me wrong, though, I'd vote for a hole in the ground before I'd vote for the incumbent.