Sadly I'm still pretty sure the most damage here has been done by Ukraine itself:

Yes, of course there are some nazis in Ukraine. Sadly every country seem to have some fringe right-wing morons. And using them to fight Russia, especially in a time when the offcial army wasn't up to the task yet, was understandable.

But that's not the main problem. The main problem is doubt that Ukraine will be able to handle them at some point when it's necessary. And when -to paraphrase Ukraine's then ambassador to Germany for example in 2015- the answer to the question if they realize that this can become a problem down the road is: "No, you are lying to help Russian propaganda! There are and never in history were any right-wing groups in Ukraine!" that's a pretty big indicator that they won't manage that problem ever. Because acknowledging it exists would have been the required first step instead of spewing insane rants.