> So abducting the leader of one country (against international law) and killing the leader of another country (against international law) is fine?
Depends on the leader and the country. Abducting or killing Hitler would be fine. The problem in this case was that killing the leader isn't enough to change the regime. But the regime is objectively evil and much more so than the US.
> After a certain country shredded a nuclear deal and made it increasingly hard for international organizations to do inspections.
Fair point, but the issue with the previous deal was that it forced Iran just to pause the program. Now they're possibly invulnerable and it may be the case that there's no way to stop them from developing nukes. The regime should have been removed when Iran didn't have thousands of ballistic missiles.
I agree with the evilness of the regime. However, the problem is that when individual countries start to decide who is evil and who not, countries just declare someone evil when it is convenient to them ("there are nazis in Ukraine!") and you have a pretense to invade a country.
International law and organizations exist to avoid this issue. But the US and Russia (and maybe China) have been systematically undermining international institutions because they like to be able to attack someone at their convenience and not be held responsible for it.