While Google's slogan may be "Do no evil", they greatly encourage others to do their evil for them. They remind me of a pimp that sits back and makes money, while all the street walkers do the work, get beat up and get arrested, while the pimp counts his money.
What I'm talking about is Google's importance on links. While the theory of PR and link popularity is a good one, the reality is it's turning those of us into SEO into link whores.
We all must go out and get links to have a chance at Google traffic. And in order to get links, we need to be on others' sites.
99% of all the link spam in your forums and blogs is due to this simple point, that Google will reward a person if they get links. And this is now greatly affecting many, many inncocent bystanders that run forums and blogs, who are becoming the collateral damage.
I wonder if there may be a "revolt" against this in the future? Truth is, if Google didn't reward this behavior, there would be far less incentive for anyone to spam your forum or blog.
We can keep coming up with anti-link spam measures, but it will never end as long as Google keeps rewarding folks to link spam.