Putin wouldn't have allowed them to become members. And this is effectively what is happening here: Putin is unfortunately destroying Ukraine, and effectively making sure that any possibility of joining NATO is long gone. This would have just happened earlier if Ukraine had tried to join NATO.

From the Russian point of view that's your mortal enemy that has expanded for the past 20 year and now it's knocking on your borders. How would the US react were Canada, an "independent, democratic country", "voluntarily joining a defence-alliance" with Russia that allowed Russian military to place missiles right on the US border?