"all these shouters/catcallers are the women police" - That's it, chibi. Bollocks to us "policing" men, the abusive ones are keen to let any woman know - whether she be old, young, pregnant, thin, fat - that walking down the street is never just walking down the street for them, it's displaying yourself for public comment. They are keeping us in our place, which is defensive and slightly scared apparently.
Sometimes I do get the complimentary type "you're beautiful" or "you have a lovely smile" or whatever. This should make me feel happy I suppose, but it doesn't because a) I'm always afraid of what the end of the phrase will be, e.g. "you're beautiful, I want to fuck you right now", and b) the nice commenters just remind me that my face, features and figure are apparently up for discussion at all times purely because I'm walking/sitting on a bus/shopping whilst female. And that makes me feel exposed and like I just want to hide away in my house and not go out at all.
It's totally different to being complimented on a night out, or by a friend or acquaintance. And it's totally different to being chatted up, where presumably the man is hoping for a positive response. A man leaning out of a van window and about to drive off, or shouting at you from the other side of the street, is not honestly expecting you to turn around and say "oh, you want to fuck me? Thanks so much, I'd be honoured, where can we go?". In fact in most cases if you did do that they'd already have driven off/passed by etc. They don't want a response, they are telling you that you are being watched.