Probably most importantly, the negative trust being left by some users is diluting the effect of negative trust on actual scammers, which has resulted in multiple instances of scammers being able to scam
Oh QS, the already-proven scammer, constantly pulls this bullshit claim out of his ass.
Let's see which sounds more likely:
1) A forum member is considering the post content made by another member and notices they have red text under their user name. They click through to the trust and read why this member is not trusted. They decide for themselves how the rating may, or may not, be applicable to the evaluation they are making of that member's post.
OR
2) A forum member is considering the post content made by another member and notices they have red text under their user name. They decide to ignore it and just trust the content of the post and/or the legitimacy of the link in their signature because they have seen other members with red text under their user name so, you know, it doesn't mean anything, right?
[EDIT]
The existence of trust score is undermining the importance of actually reading those trust feedbacks.
Actually this is far more likely to be a genuine issue than QS's nonsense claim.