The negative side is that some of these people tend to be biassed towards other members that do not belong to their group.
This may be the case for a minority of users, but in general, this isn't true. People who make very good and merit worthy posts generally
consistently make high quality and merit worthy posts and therefore earn more merit, which is why it seems there is some sort bias for their posts, when in reality it's just that their posts are consistently high quality. I generally pay very little attention as to who has made a post when deciding whether or not to give out merit. In fact, if I do pay attention to the user, it's usually to skew my decision making in the opposite direction to that which you are suggesting - when I am down to fewer than 10 remaining sMerit to hand out, I'll sometimes skip high quality posts by high ranked members or members who I know I frequently merit, and instead opt to "save" my sMerit for newbies and other lower ranked members.
I have seen lots of merit worthy topics and posts but garners less merit because this member is not known to them and they preserve their smerit to their so-called "friends".
Please post links to them in this thread:
[self-moderated] Report unmerited good posts to Merit Source