It may well be their "choice" but is it our choice to have their tits shoved in our faces on the train or the tube or in work and have our children pick up discarded copies of the Sun and see girls with their tits out? Plus, it does perpetuate the attitude that women are just there to be sex objects and men carry their attitude with them into the workplace and at home. If you've looked at the voting comments, you'll see that Rape Crisis have signed it.
As others have said, we don't live in a vacuum. And, in answer to the point of there being other things to worry about, it's not either/or. We can worry about Page 3 and about FGM and other abuses directed at women.
Is it not a little ironic to tell me what I should and shouldn't be doing after telling me that I shouldn't interfere in the choices that other women have supposedly made?