«would it not just be wiser to execute all three of them and be done with it?»
Haley countered that with "Sh'heah, right" and then went to explain why that would not solve the problem. Being wrong or evil wasn't one of the reasons not to do it.
I didn't see any member of the order complaining about killing the prisoners per se, just about how pointless that would be. And they didn't take them to court either, they were sent to life emprisonment without trial. OOTS have acted has law enforcers and judges before.
V has been on this boat for long, it's not just the fatigue. This wasn't really out of character, menacing Elan yes.