I think they should be held responsible. But, frankly giving them neutral/negative feedback isn't going to hurt them as evidenced by a few campaign managers still running campaigns even if they've pulled off something shady.
- banning joining applications in bitcointalk, use Google or external service or
- manager should create a separate self moderated topic for applications (if he didn't want to use Google ofc) and manage it accordingly.
That only addresses signing up for campaigns though, and doesn't address the problem that some campaign managers are encouraging spam by allowing anyone to join up, and not review their posts at the end of each period.
Having said that I think it's about time that all applications are done off forum, and make that a requirement.
What about manajers that are Junior members or buy their way in with Copper Membership... they don´t care about the user, just want to do the campaign and go.