Without even signing up for Linkedin I could tell they were a spam factory. I was getting incessant sign-up emails because a friend was listed and made the mistake of giving them emails of his friends. I yelled so loud I think Linkedin must have put me on their blacklist, as I've not seen a peep out of them since, and that was several years ago.
Recruiters are just another form of telemarketer. I remember a good one or two back in the 1980s, but if they still exist they're well hidden. Fortunately, I've been around so long I have no need for such foolishness-- I know enough people now if I were to need it, I can find out about good jobs via word of mouth or personal email. Certainly any place that only wants fresh grads is going to be a place only an actual fresh grad would ever want to work, and even then only long enough to build up a resume.