The older I get, the test for me on foreign involvement is a simple one: would I have gone and fought this war - or (if older) would I want my son or daughter to go fight this war - and now with a 12 year old grandson - I ask if I would want him to go and fight this war. My father joined the service in 1944 and spent large parts of two years in a German prison camp after being shot down over Eastern Europe. To this day he regrets not one day of his service and is happy he went to help save the word from fascism. I would hope I would have the courage to do the same thing and my kids and grandsons would do the same.
But aside from WW2 - I can think of no war in the last century that merits that personal test for me.