It's the equivalent of Iran murdering Pompeo. Would that be acceptable to you?
In fairness, it's not really.
Soleimani was a ranked General on the ground ordering specific military interventions.
The Quds force he directed oversaw direct combat operations and assassination plans (actual ones, like targeting ambassadors) including those against the United States military.
He's likely a fair military combatant at that point as much as any ranked General in the United States rolling through Afghanistan or Iraq.
There's questions about drone legality and the constant moving fence of "defense" when attacking to prevent an upcoming assault. There's the consideration of benefit of the target. There's our lack of status of forces agreement with Iraq which is constantly shifting. But trying to twist a ranked general commanding on the ground interventions into a Bureaucrat only isn't truthful.
Also, since you raised the specter, in countries where the CIA has chosen and funded a side in a civil war (lets say smaller and/or losing side), if Pompeo showed up and the other side killed him, I wonder what the legality would be.