That's a fine position to hold. The question is...do you trust the Ukrainians to not pick a fight with Russia, thinking they have the US and NATO at their backs?

An odd concern to have. Every other NATO country has the US and the rest of NATO and their backs, and none have chosen to attack another nation - even though they adjoin countries that are much less powerful than Russia.

But if that's your concern, again Taiwan might be a constructive example. Our posture towards Taiwan is one of "strategic ambiguity" - a strong enough commitment towards defending them that it has dissuaded China from attacking, but one that's subject to enough US discretion to dissuade Taiwan from declaring independence (much less declaring war).

It's not hard for even modestly skilled diplomats to craft a policy that would signal to Russia that aggression against Ukraine will be met with an overwhelming flow of resources and materiel for them to defend themselves, and also signal to Ukraine that if they get into a conflict that they started that they'll be on their own.

en.wikipedia.org - Taiwan Relations Act