I do not see any reason why it should be illegal to bet on sports. Sports are fun and they generally have an outcome, some of which can be measured by odds. This makes sports the perfect game for betting. Many people enjoy gambling and I think it is fair to allow it, so long as it doesn't interfere with the game it self.
For normal people to be on sports should be legal because it is good fun, it promotes business, and it generates a lot of economic movement. However, there are problems of people who have a vested interest or ability to influence the outcomes of sporting events trying to bet, and that should be illegal.
I personally am not a gambler but for every gambler that takes it too far there are plenty that like to place a bet here and there socially to have fun. I see no issue with somebody throwing $50 on a game that it doesn't hurt them if they lose it just to make the experience more fun to watch.
It is all in good fun. As long as people do it the right way it should be fine. Just bet while at the place and not underground through criminals. If we allow sport bettings than that will keep people from doing it the illegal way because they have a safe option.
No, it should not be legal to bet on sports, because that would lead to too many people cheating and throwing the game. Sports would become bigger business than they already are. Athletes would face tremendous pressure and might also receive threats. Sports are better left pure, where they are only played for the fun of the game.