Brass, while interogating Carl, was very biased. Carl, even while a person with an 'issue', still deserves to have his comments taken down and to be treated like any other victim, until they become a suspect obviously. Even then there is some professionalism expected.
I think, though, that Brass's scenes were meant to be intentionally rude like that. They probably gave the lines to Brass rather than Sofia because Brass can make being rude incredibly funny. And also, even if you've been appointed a job you're supposed to be neutral at, your going to have biases. And for a lot of people - especially people with children - pedophiles aren't even human at some point.
Combine that with the fact that two little boys went missing around his neighborhood, and it could've been that Brass just didn't believe him.
But yeah - pedophiles probably wouldn't get most peoples' sympathy. I'm not saying that's right or wrong, but they violate a taboo so deeply engrained in society that most have a hard time forgiving that.
And that's the other question - should they be forgiven? After all, can they ever consider themselves "cured"?
In Carl's case, it was a resounding no. Obviously this is TV, and it was played for drama, but they were making the point that even someone who attends therapy, who helps the police... even they can relapse. And how long would it have been before he touched Lucas?