[Always *]

Is it wrong? No, not on a fundamental level. Is it bizarrely overprotective? Yes, especially considering you are 20. I mean, it'd be a whole other story if you were like 9 or 10, but then they probably shouldn't be leaving you at home alone.

Given that you're 20, I think it is suuuuuper weird that your parents won't let you go out with friends or have friends over if they're not home. Have they ever given you a reason for this? Would it be a different story if you walked to some landmark (park, grocery store...)? I ask that because I wonder if they have reasons to be wary of your friends or your whereabouts and if they just have a problem with your friends being at their house.

Talking to your parents calmly might be a good start. Pointing out that you're an adult might go a long way (or not). It's a difficult thing to be an adult child living at your parents home; on one hand, you don't have to listen to them, as long as your actions are within legal / moral / ethical limits (whatever you abide by), but at the same it is their home and it just seems respectful and reasonable to obey their rules (preaching to the choir - I lived at home for a few months when I was 19, after being on my own for the better part of a year and I was losing my mind. Because of that, you might want to find a way to compromise.

If there is no compromising (or total change of minds) to be had, is there any way that you can move out? If you don't have the financial means to do so, of course, wait, but maybe you can work on getting the financial means to do so. There is loads of cheap housing around - many of my friends pay about $450 a month each for their homes with roommates, the place might be totally scummy or you might have to live with 3-4 others, but if it means you're out and free, then it's some place to start.