In response to the question "will the U.S. be installing up a no-fly zone over Ukraine?", Pentagon press secretary John Kirby has a simple, short answer: "No."
He doesn't elaborate further. I can't speak for Kirby or the interests that he represents, but feel that his position must have something to do with avoiding the cessation of human life on an unprecedented scale.
It's useful to get him on the record, so criticism of the question and the person asking it is misplaced. There are a lot of people, including journalists and celebrities dreaming away in media la-la land, who genuinely think that the U.S. should attack Russian forces directly, even if it risks nuclear war.
Here, for example, is Richard Engel:
These guys live in floating worlds—Twitter, the Beltway, newsrooms, their own careers— and have little attachment to people outside the stories of their lives and others' deaths. Buyer beware.