Well that's an argument for sufficient oversight and well defined limits on how it can be used, which I definitely think we sometimes don't do a good enough job with. But abuse isn't inherent in the capability, I'd argue, just inherent in a poorly managed system with no oversight.
What process could possibly prevent abuse, given our constitutional design?
From the creation of the CIA when its first operational assignment was the terribly inappropriate response to British Oil's request to do something about Iran wanting more money for oil by overthrowing their government and installing a reluctant dictator, giving him a brutal security force which harm to this day, through Reagan sponsoring terrorist armies and such and much more, we've had 'oversight' - and it doesn't work.
A president doesn't get much more 'trying to do right' in policy than JFK, and yet he participated in an illegal invasion attempt and attempts to assassinate (his CIA likely involved in the assassination of the UN Secretary, likely without his knowledge IMO I needn't list examples for president after president.)
Oversight doesn't prevent these things - but I'm not saying it's worthless, it has benefits and can reduce abuse - but it's not enough.
If it means they think through committing acts of war against the US a bit more carefully, then that seems like a GOOD result to me.
It's not like you to be that silly. This isn't about that. We have a military that deters aggression, you don't need to assassinate for that.
Assassination is something that deters something far different than 'committing acts of war against the US'.
Look at the history in the last century. The most common pattern of our going after a leader was his refusal to put US corporations ahead of his people's interests.
Read 'Confessions of an Economic Hit Man' for examples. Read Smedley Butler's summary of his decades in the Marine Corps on missions for corporations.
I mentioned the removal of the leader of Iran for cheaper oil. Look at Chile - for daring to stop allowing a US corporation to hugely exploit it by taking its copper, its number 1 industry, out of the country for a very small payment. Take a look at our coup against Hugo Chavez, for refusing to allow US corporations to have too much in their economy (there are various complaints about him but that was the trigger IMO). Look at Aristide in Haiti, look at so many Latin American countries who stood up for the poor.
I could go on, but the point is how assassination not only fits abuse far better than the benevolent use you mention - bin Laden was not deterred by the treat of assassination which did exist, either - but it encourages the abuse of power, silently dominating the relations with leader after leader not against aggression, but for economic abuse.
LBJ had a good quote on this as he learned what was happening - 'we've been running a damn murder, inc.'
Each nation should be completely free to engage in whatever kind of acts they want on the world stage, but it seems unreasonable for them to demand a lack of consequences. And as far as deterrence goes, dropping a smart bomb on some tin pot dictator seems a lot better than killing thousands of his people who probably have no more wish to be fighting us than we do to be fighting them.
Just as torture always tries to justify itself with the ticking bomb scenario that isn't what actually happens and, if allowed, becomes abusive - ask Israel, whose high court approved very narrow circumstances and couldn't prevent them from turning into widespread abuse far outside the rules - you can just assassination with some benevolent scenario about how it prevents a broader war.
And that is tempting, when you see the horrible cost of an evil leader (never one of ours, of course).
But open the door, and you have a lot of unintended consequences.
It's like the argument with a libertarian about all the fantasies he has about big corporations will behave nicely in the system and there are these wonderful remedies like lawsuits, oblivious and naive about the disaster the policies would cause, forgetting 'absolute power corrupts absolutely'.
Since Reagan's order - continued by each President - we aren't doing so much assassinating and terrorist armies in Latin America and such.
It's not hard to fall back to that, with a President Bush, Trump, Palin, Giuliani with these options back in place.
We're enough of an empire already, without the use of assassination to further force foreign leaders to do our bidding outside any legitimate pressure.
I'm not convinced the abuses are outweighed by the benefits, and not convinced by cherry picked scenarios that the abuses won't happen.