The world has been, is, and has long been a cluster-f@ck. For each of your questions, the potentialities of our non-involvement look at least as bad as our involvement or worse.
An unchecked Vietnam/China might have looked further in Indo-China without US involvement in Viet Nam.
And the likes of Khadafi, Assad and Saddam Hussein were certainly no stabilizing influences in their regions . . . . Their very existence was the cause of our and international problems for decades.
Hell, maybe we blew up The Maine in 1898, (isn’t that the latest Alt theory?) but I’ll bet my bottom dollar the people of the Philippines have lived better for our decades long commitment to fighting their Commie and Muslim radicals, and then the Japs.
Hey, maybe we can agree on just how badly the Russians f@cked up Syria, by letting that nice Assad regime collapse, creating instability in the region. Had Russia not had such a heavy investment in Ukraine, they could have saved their beloved Assad regime, but have wasted 3 years, 600,000 casualties and billions trying to take out a Ukrainian-Jewish President they claim is a Nazi.