They know full well that it means no NATO application is possible or else they get taken over as simply as the Donbass and Crimea did.
The Donbass reaction will be what? A strongly worded response? Some ineffecticual sanctions with loopholes? No one will offer Ukraine NATO membership as that means they might have to fight. We lost this already and just have some protesting to hide behind.
Beating Russia is not via conflict but through stopping the kleptocrats in power and tying the country into the west via economic means and westernizing them into the fold. Dictators lose grip eventually, even Putin- that should be our target point.
I disagree with most of this.
What is the Ukrainian reaction going to be if the LPR and DPR are recognised, with most of the Russian Army already mobilized and ready to invade the rest of Ukraine? They are going to have to accept that they are gone regardless, as they already mostly do, and saying they accept that is only going to help with NATO membership.... and I don't think them getting in would be a long drawn out process, it is more likely to be just announced to prevent the sort of Russian response we have seen.
Yes, NATO doesn't want to fight but the threats coming out of Russia have been so serious and so explicit that NATO might just accept the risk and decide that if there is going to be a conflict its better to have it now rather than after he's occupied the rest of Ukraine, the Baltics etc.
WRT the last sentence though, I think that "tying the country into the west via economic means and westernizing them" is actually what the driving force for these antics is; as Russian citizens watch the rest of Eastern Europe go into the EU and slowly start to prosper it does fuel talk of wanting that for themselves. We saw this in Belarus in 2019 and we will see it in Moscow, too. The kleptocrats know what that means for them, hence this madness.