Are they trying to legally or morally justify those attacks?

Last year I would have said that Israel was reasonably well behaved and Hezbollah and Hamas’s rockets fired into Israel were utterly unjustifiable terrorism and served no valid military purpose.

It seems like Israel is busily lowering itself it to its enemies’ level, and it’s not particularly clear that its attacks serve a legitimate military purpose to a much greater extent than Hamas and Hezbollah’s.

Compare to the US’s war in Afghanistan. Regardless of whether one believes that the war was a good idea or we’ll executed, at least the US seemed to be trying to make Afghanistan livable for its non-militant residents, and they perhaps even succeeded for a while.

Nothing, they are unguided and not targetable. They have almost 0 military value as far as targeting goes. They're "lucky" if they hit something outside of Gaza. You can see them being used for distraction/confusion (like on the morning of oct 7 in a mass firing), or as reprisals for IDF massacres (for deterrence, not working very well at that either), or for "we targeted grouping of soldiers" in Gaza envelope (usually unsuccessfully). Only thing they ever target successfully is the hearts and minds of Palestinians horrendously victimized by Israel, some of whom can feel that something is being done, I guess.

They're certainly not used to target any specific buildings in Israel. Only thing with targeting capability that Hamas ever repeatedly showed successfully used in videos is their home made Yassin-105 RPG shell and other RPGs. And these are used as short range defensive weapons, pretty much.