But they can't, and people see it for what it appears to be: illegitimate.
During the Revolutionary War British officers were aghast when American soldiers deliberately tried to shoot British officers during battle. It was considered uncivilized by the British to do this. People fight back any way that they are able to. It’s convenient for the superpower to say forms of warfare or striking back are “illegitimate” when those forms are contrary to how they want things to be fought.
It is not illegitimate for Iran to fight back the only way they can.
I think you can reasonably argue that, but (I'm guessing) that most people will disagree with you about the legitimacy of attempting to punish the USN by accosting unrelated merchant ships.
During the Revolutionary War British officers were aghast when American soldiers deliberately tried to shoot British officers during battle. It was considered uncivilized by the British to do this. People fight back any way that they are able to. It’s convenient for the superpower to say forms of warfare or striking back are “illegitimate” when those forms are contrary to how they want things to be fought.
It is not illegitimate for Iran to fight back the only way they can.