I also did a persuasive speech in favor of hunting last year. My 3 main points were population control and revenues like you said, as well as the fact that the animals we kill and eat live much better lives than animals from "factory farms" that live in captivity their whole lives, which is where most of the animals we find in grocery stores come from. This point doesnt really support the fact that hunting is "necessary," but maybe ethical and perhaps you can fit it into your speech. Good luck