Depends. Friendship anders absolutely, he's a murderer and cost the lives of many people and made already unstable [but fixable] situation explode. He is also stoic about it and says it had to happen. Sins may be forgiven but crimes require punishment, and killing him is merciful considering he's an abomination and will be killed or worse made tranquil at some point.
Rival anders, well it's clear he isn't in control of his faculties. You can actually convince him to try and talk out things but Justice takes over and refuses, and when Alistair returns he has absolutely no idea what happened. He also says fearfully of losing hours or days at a time.
I have a much tougher time killing rival anders. He was an angry guy but was also nice and not unreasonable. Justice made him completely nuts and the whole situation was pretty unfair. Worse part is he implies that he will commit suicide afterwards in the hopes of his friend Justice being freed and uncorrupted by Anders' mortal mind.
it's pretty messed up. When you meet him he just went around healing people and taking care of refugees. That was the real Anders, and that guy did not deserve to be executed. A tragic fate to be sure.