Why do some people have to believe every crazy idea?

Well, for starters, there was once a time when people who thought the world was round were crazy. People often considered great thinkers like da Vinci, Einstein, and Edison to be crazy. They had bizarre thoughts that few people of their time really appreciated. Now? Not so much. We consider them to be geniuses who were ahead of their time. 

So, who's to say that your crazy thinkers with all kinds of bizarre beliefs really are nuts? Maybe they know something you don't. 

The other thing is that many concepts are closely interlinked. If I favor socialist philosophies, I'm going to like socialized medicine, dental care, education, and more. If I'm a libertarian, I'm going to oppose all those things and will probably be against most government involvement, simply because I value personal responsibility and want minimal government involvement. There are all sorts of core philosophies such as this that we base everything around. 

At a glance, I couldn't think of a link between climate change and gun control/ socialized medicine. Not wanting gun control or socialized medicine is obvious- the libertarian would want to limit the government's involvement. So, I poked around to see what libertarians are saying about climate change. Here's a link if you're interested. https://niskanencenter.org/blog/libertarian-principles-climate-change/ The gist is, they feel that there's not enough evidence to prove it, and without substantial evidence, no changes should be made. But, I think the real kicker here is that, if they acknowledge climate change, they're basically giving the government an opportunity to stick its hands into something else, with all the trappings that comes with. Sure, it sounds "crazy," to some, but the link as to why they would deny becomes a little clearer when you start to follow the thought process. You don't have to agree with it, but if any issue can be boiled down to government versus autonomy, the true libertarian will always go with autonomy. And, the true socialist will gladly accept more government oversight if it means "betterment" for the people overall. 

I actually had several lengthy discussions with a libertarian once, and he claimed that basically every socialist policy was harming society as a whole because it made people more dependent on the government.  He firmly believed that if the government just stepped out of everything, everyday people would jump in and fill the gaps that were left. i.e. The homeless wouldn't need shelters because people would have charity and open their homes to them or donate money to run private shelters. Government food programs would be unnecessary because people would donate, and those who really could work would go back to work. That's why I put "betterment" in quotes. The socialist sees government services as necessary and helpful, while the libertarian will see them as harmful. We see these debates played out every day, but not necessarily by folks who fit into perfect philosophical slots. When we talk about welfare in America, many people think it's great and services should be expanded to help those in need. Others want reform and cuts, to ensure that the services can't be abused. Others want them gone. And, there are shades of gray between them all. Your example involves the polarization of beliefs. Nothing more. And, they only sound crazy to you because you don't share their core philosophies. 

To be blunt, it's always worth a listen, even if you disagree. You can't find common ground or inspire change if you don't ever open up a free-flowing non-accusatory dialogue about why they feel the way they do. There is evidence that backs up libertarian beliefs. It's not sufficient for me, but that doesn't make those folks crazy or their thoughts crazy. The truth is always somewhere in the middle anyway.