Ok then we should definitely fix that, might be hard to have arbitrary params survive a SSO login through an external login provider, though.
The problem with your proposal is that we would need to maintain a database table with a unique unsubscribe key for every single email we ever send (do they ever expire?). That’s a pretty big set of feature / memory / disk bloat. And it still doesn’t solve the problem that anybody could unsubscribe you at will.