Life is most definitely not "punch who you want"; that's illegal and will get you thrown in jail. There's a specific rule against that in most places.

In certain designated areas of life, such as during a boxing match, the rules are different: if you're in a boxing match, you can indeed punch someone, and you won't get thrown in jail or suffer any other sanction (other than being punched back). A boxer who punches his opponent in a boxing match is not a jerk, because that is permitted by mutually agreed upon rules in that context.

In the case of the cards, the rules do explicitly allow paying $0, so it's in no sense a perversion of the rules, and people who paid $0 are not jerks.