How Do Defence Attorneys Deal With Defending Evil People?

Hello, this question just popped into my head and I hope I've phrased it correctly. I was reading up on the case of serial killer Robert Pickton, tl:dr Canadian serial killer, with damning evidence that he was certainly capturing and brutally murdering vulnerable women. Even after he was sentenced to life and there was no doubt as to his guilt, his attorneys were still filing appeals on his behalf. I understand this is their job and there's due process/ people have rights to legal help, 100%. I just can't wrap my head around how somebody's job could be to go above and beyond in defence of a truly evil person like this who they themselves know is deserving of imprisonment. It's their job and defending that person isn't an endorsement of them, I'm just baffled by how people deal with this, I would find it immensely difficult.