My two cents:
While I don't recall seeing any thong-bearers on my last (and only one so far) cruise (the Destiny) last March, I don't see the problem with it either. To put my comments into perspective, I am a female that, at least I believe anyway, could wear one if I desired to and look nice, but will not be wearing one on my Triumph cruise because I choose not to.
I have to say that if I were to wear one, I would not be doing it to offend families and wives/girlfriends/non-thong wearing women. I would be doing it because I felt proud of my body and/or didn't choose to have tan lines and/or for the comfort of it (they don't obviously bunch up or otherwise mis-aligned). Additionally, if I were with a bunch of my girlfriends on spring break and they also were wearing them, I would feel even more comfortable as there is always strength (and comfort) in numbers.
As a girlfriend who will be traveling with her boyfriend, I'd honestly have to say that the only reason why I'd be uncomfortable with a thong bikini-clad girl is if I felt insecure. And maybe we all feel that way at first. But if you just get over it and enjoy your own darn vacation, one may realize that a thong alone can not offend or shock the family, it is one's attitudes/feeling towards it that will make an otherwise shockless moment a blemish on the cruise experience.
In the end, if a pretty female is wearing a thong, or any other flattering piece of clothing, a husband/boyfriend/male is probably going to look. Hell, I'd probably notice too! It is human nature to appreciate beauty in all forms. Keeping in mind that beauty is in the eye of the beholder, some males may not even be interested. If we remember that we can not control everything and actually accept those things that we can not control, our own personal lives will be that much better
Don't sweat the small stuff....it's just a bathing suit!