It's a very divided thread, pitting bean & fellow ignorami and DU-members who at least "get" that the result would be WW3 (and maybe have seen a map and "get" that geographic realities would make US and NATO efforts more difficult).
I do not want Putin to get back a big chunk of the Soviet empire. I also do not want WW3 with a main theater in Russia's logistical backyard. This, IMO, limits US/NATO options to what would not result in WW3. IMO, an air-to-air-missile-enforced "No-Fly Zone" would likely have that result.