So, you can get a negative reputation tag just for applying for this campaign?

I mean, if this a known scam, ban them, close the thread but why should you punish the users just for trying to earn some $$$?

That's because you are promoting a known scam by joining their campaign. It's guilty by association. Banning is never the solution, if they want to be here, let them. Just spread awareness about the accusations against them.