What right will we have to criticize Putin if he kills Ukrainian president Zelenskyy?

From a legal standpoint, the US has illegally killed the leader of Iran in an illegal war which our leaders are not even criticizing. They are just accepting that the US takes out a leader they do not like, thereby destabilizing a nation of 93 million people.

International law does not allow this, but if we do not uphold international law, what boundaries do we have left to limit dictators like Putin?

@randahl I lost track as when we stopped holding Politicians responsible for their actions or failings. To an extend in some countries this still seems to be the case, but under the line it's a very disappointing result.
After all; these people are supposed to represent what the majority wants or at least agrees to (to an extend).
In my brain, just arond covid things started to go sideways very fast, very extreme - but I may just have been to occupied with myself before that...