I think the reason why Russia hasn't used nukes, and will likely not do so, is fear of drawing NATO into the conflict. But if NATO or just the US does send troops or planes to Ukraine, and start directly attacking Russian troops there, then the cat would be out of the bag and there's no reason for Russia not to start using tactical nuclear weapons or hitting NATO/US targets outside Ukraine.
The cat needs to stay in the bag, so that there are some unknown, unpredictable consequences that the West can threaten Russia with. When those consequences are activated and become predictable, their value as a deterrence is going to plummet.
So I don't think it's worth the risk. I can't answer the poll though because it doesn't have an option for "we shouldn't send armies to Ukraine even if Ukraine is losing".
I think the chance of Putin escalating to nuclear war is extremely low. Perhaps if coalition forces threaten to attack into Russia. But I don't think that's in the cards.
The only problem, of course, is that when it comes to nuclear war, even a low chance of it is perhaps an unacceptably high risk. But at this point
On a general note, sending troops to other countries and fighting on their behalf is usually not a good idea. See Afghanistan: the locals just decided to swipe the money and sell the weapons, and let US and allies do all the fighting, because they could. It's a bad incentive structure. In Ukraine, the locals are the ones who have to decide, when they've had enough, and we need to give them what they need to get as good a negotiating position as they can get.
Finally, an actual serious argument against a war in Ukraine. I think the main problem with the Afghanistan invasion was that the narrative USA was telling about itself was a complete fantasy. Nobody sees USA as the land of the free outside USA. The cold war tarnished USA's image beyond salvation. Something Bush Jr failed completely to understand. It was a question of mismatched propaganda narratives. To the Afghanis I'm sure USA's rhetoric came across as the ramblings of a madman. Which is fascinating in its own right, because nothing should be easier to win against in a propaganda battle than god damn fucking Talebans.
Ukraine is different. But Ukraine is ruled by Oligarchs. Zelenskyy is just a puppet for the maffia. We don't want to go war only to hand it over back to the Ukrainian oligarchs/maffia once it's done. But we do have a golden opportunity to help Ukraine become a modern nation with low corruption. Also a good idea because the Ukraine has natural gas. Making us less dependent on Russia for it.