The primary issue is that it begins to supplant the userbase. When you look at the front page, it wouldn't be content from the users- instead it would be content from these people. Discussions the actual users want to have get shoved to the bottom, are seen last/less often, and/or are disregarded due to low score. As new people come in, they'll look to the people with high scores for what the community looks like. The perception will be that the high score people are the major movers and shakers and have earned their points legitimately- in reality they're people who have gamed the system. The perception will be that the subset of the userbase begins to look like the majority of the userbase. In time (especially with these same 'cheating' individuals having alts who have also cheated) they'll look like a vocal and active minority (or majority depending on activity level of the site). In short- the site might be good, but the shills are always shills. The shills will drive off new users by foisting bad content/creating a bad environment. The shills will drive off the old users by preventing them from having conversations, old users having fatigue from dealing with shills, and a perceptible lack of growth of community. The shills win when there is nothing left except for shills.