I think if anyone wants to suicide, it's their responsibility, and it's not okay to bring someone else into the choice and not give them a choice about it, too.
Cops are humans too. I grew up in a family of cops and while I no longer have much respect for law enforcement, the ones I knew never wanted to kill anyone, and I never knew one who did, though I did know a cop who was killed. In twenty years my father never fired his gun except for at the shooting range, it was always a last resort measure. Of course I'm 49, and the culture is very different now, but you'd still be taking a chance that the officer could be traumatized for life by being tricked into murdering someone. Same with a train conductor, a truck driver or someone driving a car. The cop would have to face your family, face an inquest, possibly go through therapy. They would learn about you afterward, who you were as a person, you would become real. They would never forget you. That's a lot to put on another person for the sake of convenience, even if they were a total trigger-happy asshole, and you have no way of knowing if they are or not. They could be totally decent, have a husband or wife, have kids, end up on the news and villified, their kids villified by their peers, experience so much social pressure they have to move, and one day maybe end up suicidal over it.