And many jobs involve taking risks. Investment houses. Sales. etc. We reward those who take risks because society (often) benefits.
I find it much easier to argue against standard casino games because it's pretty easy to mathematically prove that the gambler will end up broke. With sports, it's a bit harder. As long as the vig is small enough, smart gamblers who know the teams can eke out a profit. If anything, sports gambling rewards study, thought, and focus, all things we should celebrate. THat doesn't mean I like. I would like to see it banned. But it means I have trouble arguing against it with any vigor.
It is true that the casinos will find a way to ban people who find an advantage in traditional games like blackjack (think card counting), but that's different. In sports gambling, the profit is extracted with the vig/spread.