from what i remember, many states do allow you to release tadpoles you've raised back to the wild. in my opinion the only real diseases to worry about are ranaviruses and chytrid fungus. as far as the other stuff (bacterial disease/opportunistic fungus), it's usually stress related illness due to normal flora from being in captivity. if you let them go, they're either going to die or recover and in either case you're not exactly changing the environment since it's already there and presumably wild frogs aren't necessarily going to get infected. the only other argument i can think of for not releasing is mucking with the genetics from one location to another if you release them into a different location.