From my perspective, I feel much as a couple of posters on the thread have said.
Ever since I was young I felt really uncomfortable when men looked at page 3 near me on public transport. When I was a young teen I just felt embarrassed and uncomfortable and then as I got older I realised that it's because it's just a reminder of what as a young woman some men think you are "for". Of course it's not helped that quite a few men IME use it to deliberately upset / illicit a reaction from women and girls as they know they don't like it. It doesn't take a genius to realise that sitting staring at a young topless woman on the bus while sitting next to a 14 yo girl, and pressing your leg up against her, is likely going to make her uncomfortable. Men would also sometimes look at page 3 and then at my chest which was just horrible. This was all when I was young.
Thing is that if men are having lecherous thoughts about the girls and women around them, the girls and women probably won't realise unless he does something. Page 3 is a mechanism for some men to make women and girls around them realise that. They like to use it in that way, plenty of men enjoy the discomfort they can cause with it.
For me it's just not appropriate to look at soft porn in public really. I think that people would realise this is it was any other type of soft porn. If a man sat on a tube next to a schoolboy looking at sexually provocative pictures of scantily clad 18yo boys, most people would say that was not right. But because it's a "newspaper" they say putting girls in that position is just fine.
It's not just fine, I have always hated it. To me it is a clear message that it's more important for a man to do something that he wants, even if he doesn't need to, than for lots of girls to go about their day without being made to feel uncomfortable and sometimes intimidated, and reminded that in our society to lots of people the only thing of interest about them is whether they have nice tits.
I agree with poster upthread who said "they really hate women" - although maybe more women sigh and feel pissed off rather than a stronger reaction so it should be "they really hate women and girls". And they do - they don't care one fuck that their publication is regularly used to be creepy at often underage girls - it's much more important that their reader gets his sexual frisson in the middle of a bus (wtf frankly).