I think the problem people have is the idea that the advert implicitly (heck, perhaps explicitly) suggests that your body is unsuitable for beaches if you aren't "beach body ready".
If the advert was suggesting all the lardies would benefit their health by cutting out the pies, then it would be fair enough. But what it's actually doing is giving the impression that beaches are not "for" pork-lords.
We can argue about the health benefits, or otherwise, of weight loss - but does anyone really believe that a person's weight makes a difference to their suitability for going to the beach?
I'm not bothered by the advert (though I'm not fat), but people's counter arguments don't make sense in context.