There rarely are rational thinking people in the room.
Rational people would have very little need for government at all.

There really is a "slippery slope" in human psychology, but it goes by terms such as "cognitive inertia" and "confirmation bias". Once people get an idea stuck in their heads, they tend to go with it (to their deaths, at times) even when all logic points the other directions.

Yes, it does.
I am not a chemist or biologist, but my understanding is that sunlight starts (or facilitates) a chemical process that produces Vitamin D. Without sunlight, that reaction does not happen.

But what if I AM a sociopath?

There's a lot of discussion here about private property and rights, and those are certainly relevant issues. But the more important issue of common sense is hardly being addressed.

All (okay, most) rights aside, the reason you shouldn't trespass on someone's property has as much to do with your own safety as it does with rights. When someone reacts violently to your unannounced and unexpected presence on their land, whether they had the right to do so is completely irrelevant to you... because you're f'ing dead.

At that point, rights are just a matter for the lawyers and your next of kin to argue over. Even if your side "wins", you're still dead as a direct result of your decision to barge into private property unannounced.

Rights don't make you bulletproof. Common sense goes a lot further than rights do in keeping you alive.