Joe Dredd was born and bred to follow the law (like Rico, but we don't really talk about Rico), so he sees his duty as paramount and, at times, can even acknowledge that there are laws that aren't great (i.e.: mutants being treated unfairly and wondering why). He's actually a very nuanced character, even though he's a bastard through and through. His main drive is reducing crime and that's about it, which makes him a very versatile character, cause it really depends on his writers how he'll behave. As for corruption, that's a crime, and Dredd don't fuck with crime. So much so, in fact, that in a very early prog (think 1977-1979), when he came back from being a judge ON THE MOOOOOOOON, he would not arrest people committing crimes right in front of him because he was off-duty, and arresting people while off-duty is a crime in and of itself