Search engines tend to look at your "neighborhood." You can't control who links to you, but linking to (or approving) a known spammer who posts with non-related comments and/or website links erodes your credibility. If someone comments and the spam filter activates, experience has shown that if I paste the comment into Google, I will see the exact comment displayed multiple times on many different websites. The search engines then go into a "birds -of-a-feather" mode and downgrade your content. If someone is posting the identical comment in multiple places, why would we want to provide them "free advertising space" at our expense just so we can claim that someone recognized our efforts? BUST'EM.