That's actually exactly Google's solution: they give you a set of reports and an indication of when the malware or malicious link was last detected on the site.

But I don't think that's the issue here. That facebook warning does not, as far as I know, get generated from a positive malware/spam/badness metric. It's just thrown up as a default action when someone links to an unblessed site on the web. That's what the poster doesn't like: it goes against the whole idea of hyperlinking.

But as lbrandy mentioned, this is in one rare case and appears to be the result of a bug. If this happened when most links were clicked leaving Facebook, you can rest assured that all publishers would be up in arms.

Hopefully it's a bug. But I see it routinely. It's definitely not a "rare case" by any metric I can think of.