Short Hair
One possibility is that he believes so strongly in the ideals and/or goals of the party that he will do anything to protect/advance them. The people he tortures are traitors who deserve every bit of what they get. In his mind what he is doing is patriotic and noble and good. The fact that others complain about his methods is not just irrelevant to his mission, it's a sign that he's doing his job well. And if he has to die or go to jail for it, he will do so as a martyr for the cause.
Under World. It rocks!
I'm doing something similar, with essentially-fascist government vs. La Resistance. It's set about 20 years into the future in the US, and the character in question is more than old enough to remember free speech. He's not involved for any ideology. He's joined up to crush the resistance because he believes that they're terrorists who are responsible for the bombing that killed his wife and daughter as colatteral damage. Whether or not they're actually responsible for it or it was a false flag by someone else is still being decided.
This character is essentially the captain of his political party's para-military organization.(BTW there are two political parties. The other one uses literal knights as their private army.) He and the organization don't like having people dissing the party that they serve and definitely don't like anyone dissing the State itself.
The problem becomes how do I create reasonable backstory for how he came to hate various ideas of freedom, such as free speech and political transparency.
What could possibly drive a man to such despair that he would break the bones and spirits of those that he perceives as criminals?
Of course note those around him, even the party that he serves (which usually sees this as necessary), criticize him for his ruthlessness and grudges.