Most of the Soviet republics when they broke away became very corrupt this is nothing new. Your argument presents a false argument we're not protecting Ukraine or helping Ukraine to maintain corruption or even in still democracy although it is completely arguable that Ukraine is more democratic than Russia. And arguably Ukraine has a better chance of coming out of corruption and have an legitimate Western style government than Russia ever will under Putin.
World War II ended and that was supposed to be the end of aquarium territory through mass warfare. Putin has reverted to World War II style military attacks in order to seize territory. That simply cannot be allowed in the 21st century regardless of the country were assisting its corruptor not.