That picture is fake. They've obviously photo-shopped another belly onto an older picture of her. Look at the blur around the top and bottom of the pregnant belly.
Besides, I've seen that picture in magazines before, of her coming out of a store and lighting a cigarette - it's an old picture, way before she got pregnant.
Don't get me wrong - I can't stand Britney Spears, and think she will make a lousy mother, but no sense in beating her up over something she didn't do.