"If it's going to be made legal, it needs to be justified" is troubling - it's supposed to work the other direction: unless justified, it should be _legal_. I agree with your sentiment that there should have been a deeper public debate here, but banning gambling seems obviously unconstitutional, regardless of how I feel about it personally.
gambling bans in general would be constitutional. There was a stupid technical issue with the law as written, not with the concept in general.