First, I don't think being driven by hatred for your oppressors is mutually exclusive with having a sincere Marxist-Leninist ideology. If you want to take revenge on your oppressors, Marxism-Leninism offers the means.

Second, that's fine, actually. I don't think it makes much sense to only allow the pure of heart in the proletarian revolution.

We have no compassion and we ask no compassion from you. When our turn comes, we shall not make excuses for the terror.

On the other hand, if you're saying that a lot of MLs are just indiscriminately sadistic, that's a load of shit and a repackaging of the anticommunist propaganda line that communists are just bloodthirsty, power-hungry murderers with no sincere convictions.