Having just finishing the war in the middle east, I'm sure the military complex would have a vested interest in joining / starting another conflict.
What about using a conflict to deflect attention away from a market breakdown?
What about using a conflict to drive a post-COVID recovery?
I'm not saying it definitely has to be one of these reasons, but I can think of many off the top of my head. Why are you so certain that USA or NATO nations would have no reason to start a conflict?
First you say "this is going to happen" and then courageously prevent it by something you needed to do but had no excuse before.
Ukraine is not member of NATO and not an ally of NATO states, just a rather unreliable partner in security cooperation, a corrupt democracy with stagnating reforms that does not want to commit to the diplomatic agreements negotiated with the help of the West. There is no reason for NATO to participate in any military conflict there.
https://news.un.org/en/story/2022/01/1110912 The UN reports that Russian troop buildup is happening at the border
The area has already had Russian agression via Crimea https://en.wikipedia.org/wiki/Status_of_Crimea
Are people suggesting that no one should respond militarily to an allies plea for help to respond to military aggression?