For all the people saying this should be applied to email, it already has been (sort of) with LinkedIn's InMail. Basically, premium accounts for recruiters et a

For all the people saying this should be applied to email, it already has been (sort of) with LinkedIn's InMail. Basically, premium accounts for recruiters et al. get a limited number of InMails every month. If they want more, it costs something like $10 each. The trick is that the mail doesn't count unless you actually reply to them. The end-game is that I politely reply to every recruiter who contacts me that I'm not interested. I don't make any money, but at least there's a downside for them to spam a bunch of unrelated accounts.