You keep bringing up the "abuse".
How are they going to abuse you? By ignoring you? That is an abuse?
Using the power to unlimited merit your friends (or alt accounts) while other users are withheld from receiving merit points, while they may post equal or even more qualitative posts, I call abuse, yes. It is again, like the trust system, subjectively determined by a few chosen ones.
You're only limited to 50 merits max per account per month, so i doubt that it is going to happen much.
Ontop of that, every merit you give is transparent, and i believe that there soon will be some kind of log where you can see who gave who merit points.