So, when are we bombing Israel to prevent the world being held hostage by nuke-wielding religious fanatics?
and the starting point of all this is the US coup in Iran that eventually lead to the islamists seizing power in Iran.
1982, Israel invades Lebanon. Iran backs Hezbollah, which triggers its first killing of Israelis in 1983.
There would have been reasons to back the creation of Hamas long before 1982 but the revolution in Iran only took place in 1979, so through the decades of Palestinian oppression, massacres and occupation, Iran was aligned, so it started with a support for Lebanese resistance. Then much later the backing of Palestinian resistance, then Yemen via the Houthis.
It is true there has been constant funding, and of an increasing number of proxy groups, but Israel's invasion was the trigger. Backing nations, and paramilitary groups is pretty common: see U.S backing Ukraine regular army, and private mercenaries.
As for why America is involved in a conflict between Israel and Iran, it's because we have a Republican administration and a big segment of Republicans (Christian Evangelicals) want the US to ensure Israel as a state survives (also for purely fanatical reasons).