Thing is, being martyred in the line of duty tends to increase public sympathy for a figure. So even if you didn't like him, you don't objectively stand to gain anything from a tragedy like this. Whatever he may have done wrong will now be overshadowed. The pertinent question now is, do you believe that his successor will be more to your liking or less?

And regardless what you think of him or his party, any destabilization is risky at a time when a country is at war, and Iran frankly is at war and has been since the Islamic revolution. It may not always be openly declared but hybrid economic war and war waged through terrorist proxies is still war.

I understand that he may not have been the most impressive figure or had the best policies, but when enemies of Iran are openly celebrating you just need to ask yourself why that is and whether you want to find yourself on that same side.

Personally i'm not Iranian so i didn't have any emotional attachment to these people one way or another, but i just find it distasteful for a leftist to be happy over the death of major political figures in an anti-imperialist government.