Look, I support Terezi’s justice like everyone else, but is it really validated here??
Not to say that Gamzee shouldn’t pay for what he did, but this isn’t the same Gamzee. This is the dork smiley minion for Aranea who has no control.
So what I am saying here is, if Terezi did kill Gamzee, would it bother her to know that this Gamzee had no control/opinion of her feelings/actions? Would killing him and getting him out of the way be more important that to see him recognize his misdeeds?