My DD wears those shirts. I don't have a problem with it as long as she wears a tank under it. No one needs to see her sports bra. But, absolutely nothing written on her butt. At one of the tourneys she wanted a pair of pajama pants and there was only one pair that didn't have writing on the rear.
I mean come on-show some class parents. there have been cautions out there about stalkers at some games before. Don't let someone's eyes go there. If you stop buying them they will, eventually, have to stop selling them.