Yeah, I don't think this would be a good idea and would lead to a lot of hysterical crying and possibly malicious abuse. Most scammers can't join signature campaigns anyway, but on the flip side there are campaigns that will accept them, but I don't think negative feedback should wholly disqualify you from campaigns (but this should be decided on a case by case basis).
That's a very good point about negatives should be considered on a case by case basis. I think a lot of the managers put that in so they don't have to research each individual case though. Another sigh that these people who are running these spam campaigns are lazy.