It's true the government of Ukraine is corrupt as hell.
So is the government of Chicago.
If Russia invaded Chicago, I like to think we wouldn't stand around saying "well, I dunno... remember how crooked they are," before standing up.
In a "gang war" where the smaller gang hasn't attacked anyone since the 1700's while the larger one is bombing maternity wards, shelling nuclear power plants, has displaced 2.6 million people in under 21 days and the figure is rising, and has pretty openly threatened nuclear strikes on NATO, it seems to me the larger gang is the bad guy here and let's be real: the US has never had a problem siding with a lesser evil against a greater one (nor should they have any such scruples because that's how geopolitics works).
Mao was a bastard, but we had no problem siding with him against Stalin.
Iraq and Iran were both run by bastards but we propped them up against each other to make sure neither could be a threat (until we crushed Iraq).
If Ukraine is not full of saints but they're the forefront of a showdown with Putin, well, the Army never cared about my moral character as I long as I killed Jihadis. Why should we be pickier about our allies than we are about our own troops?