I think rules and regulations for a forum should be consistent with the people that you want to attract to your forum. The right set of rules will make the people you want to attract comfortable, and make the people you don't want to attract uncomfortable and inspire them to leave.
For example, if you're trying to make a forum for Christians, banning promotion of homosexuality would make your Christian users more comfortable. Conversely, if you're making a homosexual dating forum, banning promotion of heterosexuality and Christianity would make your intended users more comfortable. That's an extreme example, but hopefully you get what I mean. Getting the right activity from the right users is what inspires forum success.
Likewise, for a forum dedicated to making money you want to attract people who want to make money, by buying, selling, posting on the forum, clicking on ads, etc. That means that you need to keep scammers and spammers out. Scammers will want to take money away from your members, and spammers waste your users' time. But if you're starting a forum on con artistry, the opposite would apply, and so you would want to make rules against the content we see on this site.
I think of it less as a balance between moderation and activity, and instead deciding what activity that you want and what activity you don't want.