I think that is what we are doing, nailit. It's difficult for me to explain, as I'm not entirely sure why I feel that way.
Porn- no problem, it's honest and (in theory) you have to at least try to find it. It's normal and natural.
The same with the Pussycat Dolls, attractive women dressing up (and they are nowhere near naked) also seems normal. If others find them "sexy"- fair enough.
Page 3 seems entirely different and more belittling somehow, as it is casually to be leered at over your cornflakes. It isn't even nakedness, just topless- and the aim seems to be to sexualise breasts. Having breastfed for many years, often in public, but always discreetly, this kind of attitude really doesn't help.
Look at any thread here, where someone is trying to feed her baby, and they are seen as everything from attention-seekers to exhibitionists. I don't like the idea of making life even harder for new mothers and this doesn't help- particularly as (old-fashioned) newspapers tend to be left at home, where children are etc.
So, not because it is "naughty"- but because it shouldn't be.