Its not always the computers fault!
You cant always throw blame at facebook or some other programs for being at fault, its called "Social Engineering" and if you send someone a link that says click here to see the woman/guy of your dreams... most infections are caused by this more than anything, some people will just click or open anything and not think twice about it.
If you give the keys to the kingdom to anyone before educating them, whats the point of even worrying about spyware/virus/bots/dDOS and so on...
But I do think facebook should have an agent that scans external links for viral activity or possible infections or scan them and give the user the option to say yae' or nae' if they want to proceed, and if they do its on there own discretion at that point.