Israel appears to have assassinated a HAMAS leader who lives in exile in Lebanon, and has hinted at the intention to do a lot more such.

I don't see anything wrong with this. HAMAS is a murderous terrorist group, so killing its leaders (or its footsoldiers) is simply war. I am skeptical that Israel could defeat HAMAS this way, but there is nothing particularly evil about trying.

The moral issue about Israel's war against HAMAS is that it is killing thousands of civilians in Gaza, and putting all the survivors in grave danger. That's what Israel must stop.