Some fish laws are stupid, but I've gotta agree with the piranha one in Texas and most of the South for that matter. We have breeding populations of Pacu and Plecos in almost every lake and river in Central Texas. Personally I'm not so scared of piranhas-people swim with them in SA just fine, but they would destroy many of our ecosystems that have enough problems as it is... However, I am very scared of the idea of breeding populations of FW stingrays here. I wade fish and deal with SW stingers down at the coast, but I don't want to have to do the "stingray shuffle" in the San Marcos River.
I know people that keep piranha and stingers and all kinds of other stuff down here from being in the hobby so long, but they are all serious hobbiests that understand what they have and the responsibility that goes along with it. It's a few bad apples that ruin the bunch, and believe me, if they were sold in stores down here someone would release them and we would have a serious mess on our hands.