Sorry, I don't believe you that what would stop those "hostile and malicious riders" is the $2 fare to hop on.

Let's use Seattle as an example. We tap orca cards to pay to get on and recently debit cards. This doesn't in fact keep the crazy people from getting on without paying at all. Only cops/security actually prevent this and most of the time we do a whole lot of nothing.

We could offer free ridership but still use orca cards and ban people who misbehave or befoul the place. Whether we keep problem children off appears to be wholly orthogonal.