EDIT: Oh, I initially thought that you thought that I was saying that it's OK for the government to coordinate assassinations but not OK for other people to coordinate assassinations. Which is not what I said, I only said (implied) that it's not OK for other people to coordinate assassinations. I made no representation regarding whether I think it's OK for the government to coordinate assassinations.
However, what I now think you're saying is that assassination markets would lead to fewer assassinations rather than more, because... if ordinary people could trade in assassination markets then they would choose to assassinate the government's assassins, and then the government would not react or respond in any way, so then the government would no longer be able to coordinate assassinations, and the general public would stop using the assassination market, and then the problem is solved. Is that right?