We invite you to read [The Steem White paper, page .14 for referance].

Abuse is defined by the opinions of stakeholders. You may consider something as not an abuse but other people might think otherwise. It is a democratic-like system that is based on stake. If the majority of the stake considers that doing X should be considered as abuse, then no one can do anything about it since this is also code. The only way to influence such a decision is by buying more stake and invest to influence the consensus.

They have the power to upvote and they use it and this permission is given by steem blockchain code.

The code of the blockchain also allows them to downvote. It does not matter if you do not consider X as abuse, such a definition can only be defined by a decision that will be based on consensus.