I disagree - I think it would be a great idea. While some may argue that gambling is a zero-sum game (which isn't exactly great, in and of itself), it's really a net loss. While some people may win a bit of money, I'd argue that the degree to which their lives are improved is much less than the degree that some others' lives are destroyed. Gambling, ultimately, being a negative sum.
> Millions of people have started sports betting. If it becomes illegal, it won't make them stop
I disagree with this too. It's substantially easier for any random person to simply tap a few buttons on their phone to place a bet than to find and arrange opportunities with others to bet on sports or visit a brick & mortar betting site. The level of effort of placing a phone bet is so small (and with 24/7 access), you'd have a very hard time arguing that making OSB illegal would only marginally impact the amount of sports gambling taking place.
Bottom line: gambling is an addictive activity for all people and some more so than others. Limiting access to it will have a positive impact on pretty much everyone who does't own or work at a gambling company.
"Offshore sportsbooks" are another thing to consider. These companies are not regulated in the US market, but still take online bets from people in the US. The ease of placing bets online does not go away with making OSB illegal. Just eliminates any consumer protection we could have had.