The problem with these spam signals, like comment SPAM, it's very hard to know if they are from the target of the links, or from some other person trying to damage your reputation online and hoping you get penalised. Google doesn't see the IPs / email addresses that submit these comments. So it's impossible to know if they are legitimate or not when it comes to who has created them.
This is my biggest problem with Penguin. No website controls who links to them. Google should do a better job at discounting/ignoring spammy links, rather than penalize a website with spammy links. It's essentially the same thing, though one is easier to come back from.
OK, but we can probably say, "many websites have not prevented unsavory inbound links". How can these sites be helped? Do they need to "referer-bomb" (e.g. how some photo sites that didn't favor image embedding used to serve goatse to unrecognized referers) these links to a "don't count this link" document? Could Google propose a standard semantics for such a document?
The problem with these spam signals, like comment SPAM, it's very hard to know if they are from the target of the links, or from some other person trying to damage your reputation online and hoping you get penalised. Google doesn't see the IPs / email addresses that submit these comments. So it's impossible to know if they are legitimate or not when it comes to who has created them.