When I first became aware of these laws I thought as you do. But after a while I came to think the laws are OK, maybe even necessary. You say “draw your curtains”, but in my example the curtains are already drawn. Unless you seal them with duct tape, there are almost always tiny holes or gaps through which someone can see, if they're allowed to do things, like pressing their face against the window, that have no legitimate purpose aside from the intention to invade someone’s privacy. Our laws routinely consider the intention and purpose behind the act.