The goal is to topple Ukraine's leadership and install a puppet who will be more aligned with Russia than the west (see Belarus as an example). An economically prosperous, stable, democratic, NATO-allied neighbor is Putin's worst nightmare.
So like the western-backed Euromaidan basically (without Victoria Nuland handing out cookies in Maidan square).
Ukrainians are the only ones who have the moral right to choose what they will be aligned with. Perhaps you can coach them or bribe them with trade (or lack of trade), but a violent invasion is absolutely not like that, it's not even comparable to what happened during Euromaidan.
Ukraine also has a corruption problem.
I think NATO will keep Ukraine on the cusp for 20 years like they did with Romania, before they allow them to join.
And madman though Putin may seem to be, he knows NATO isn't an offensive organization.
And I'm going to judge Putin by his own words. He says he's threatened by NATO on his borders? Then he shouldn't have 70% of his military on the border of Ukraine. It leaves him wide open to an invasion from NATO members Estonia and Latvia.
I think he may legit see it that way: https://www.youtube.com/watch?v=MOkl2XgZlw0
Sure, like the defensive bombing of Libya by NATO.