Utilised correctly, I can understand the logic behind it... but ultimately it's bad for forums.
Last time users were just blocking other users they didn't agree with, leading to very bizarre profile signatures and replies as they were not blocked. There was also a "karma" feature which was similar to the concept the OP is inquiring about; this too was abused as users were simply minus'ing posts they didn't like nor agree with, even if the post was a genuinely good post. I wasnt necessarily a very liked user so no matter my post, I was minus'ed to death.
The moment we start blocking other users is the moment we opt not to browse HLTV the same, it goes against the sites original premise of forum functionalities and user integration.
However, I'm also aware HLTV is unlike most websites in that the user integration is mostly unwelcome... :(