I think this is more a function of the internet than purely the legality. Legal gambling wouldn't be nearly as damaging if it was limited to sportsbooks that only allowed gambling on-site similar to how some places have handled gambling on horse racing for decades. The dangerous part is not simply the ability to bet on a sport, it's having a device in your pocket that allows you to gamble instantaneously at any time and (almost) any place.
I think the same thing applies to most vices. Any friction in engaging in the vice is a moderating influence. Someone is more likely to get dangerously drunk while drinking at home than at a bar in which you have to order every drink from a bartender. It was likely more difficult to fall into a porn addiction if you needed to look another human in the eyes when you rented that dirty VHS tape. It's easier to overeat if you're having the food delivered to your home than if you order every item from a waiter in a restaurant. When we all know an activity should be done in moderation, making it as easy to engage in that behavior as possible is probably a bad idea.
I think the same thing applies to most vices. Any friction in engaging in the vice is a moderating influence. Someone is more likely to get dangerously drunk while drinking at home than at a bar in which you have to order every drink from a bartender. It was likely more difficult to fall into a porn addiction if you needed to look another human in the eyes when you rented that dirty VHS tape. It's easier to overeat if you're having the food delivered to your home than if you order every item from a waiter in a restaurant. When we all know an activity should be done in moderation, making it as easy to engage in that behavior as possible is probably a bad idea.