Whether it's wiretapping or execution, when referencing those crimes you're making a personal evaluation of the actions without referencing any criteria for for how you judged them. To do so is to play to people's emotions about the crimes you referenced rather than the actual item for discussion, which is when wiretapping is justified, and specifically for what crime.
I view it as equally manipulative to state "we can all agree that murder is bad and wiretapping should be justified in some cases" as to say "we can all agree that changing traffic lanes without signalling does not justify wiretapping" when the actual question has nothing to do with either crime.
This is just a case of Godwin's law writ small, so it's harder to spot.
(An alternative argument is that for any extended powers of the state, we should have statistics to back them up. If wiretapping is ineffective for a crime or it's benefit is outweighed by it's downsides, maybe that should be taken into consideration. In the end, I'm basically I'm for questioning generally unquestioned positions.)