I couldn't stand to see the poor dears that way so to date I have "rescued" 3. I have since thought about it and have decided you are right, but could NOT bear to see those things sit there in their pitiful little cups so I do something that I think is a win-win for everyone. (Well, I guess so, in a way).
I make trips (pretty much weekly) to every fish store in town that I'm aware of. I thoroughly scan every single betta that's in the deathtrap cups and I pull the ones that are sick or look like they need attention and wander off to find someone who'll do something about it. PetSmart is actually pretty good about responding to my suggestions. WalMart PFFT you can't find anyone there to save your life. Other stores are pretty good about it, too - if you point them out they usually get them off the shelf for treatment.
I figure that i'll give the 3 that I've got right now a great home, and just try to help as many as I can with regular visits to fish stores and keep being a pain in their butts until they decide to just take good care of their fishes without me bugging them about it.