I would like to hear her / his arguments on why first. But i don't think i would end up marrying in that kind of relationship in the first place. But let's assume i did.

I would probably want to talk about it, as everything (or most cases in relationship) are a discussion, as there are 2 of you or more if not in monogamy. In every partnership it's important to listen to everyone involved. One member of family can't just set up rules without discussing it with others. There will be compromises and emphatic listening of others.

You can't change what your partner likes or dislikes. It isn't wise to try to control hobbies and friends either. So throwing ultimatums about gambling of all things should be explained and justified in reasonable way. At least to me. Just someone getting discomfort of me playing 5 bucks per week (if we could afford it) for example wouldn't be something i would accept as a reason. People sometimes can feel uncomfortable because someone's actions, but it doesn't always mean they should try to change others behavior.

Sometimes we need to accept each others weird hobbies we don't understand, or we don't like. If it doesn't directly affect on my daily routines, but i would feel discomfort, i would see that as a my problem. Not my partner's problem.