Sure, don't murder the guy who knows how to create superhuman soldiers and hates your guts, there is no danger that he will target your students while you are busy somewhere else or something.
Seriously, I hate this stupid excuses japanese MCs come up with to avoid killing a guy who by all rights should die and who has shown 0 intention of atoning for his crimes or not causing more trouble. I know Glenn is fed up with murder after what he went through but sparing this asshole is extremely irresponsible.