Because the invaders are already in your land, and would your rather have these "animals" released by Russia against your population or would you prefer to have them feel like heroes by going after the Russians.
Dude, stop making it personal, it's tedious.
There are no proof, nor suggestion, nor anything under the sun, that suggests, or would even hint at, Russia would release these "animals" against the Ukrainians.
As far as we know, Russia came across numerous cities. None of them got their prisons emptied and their content release into the streets.
There is nothing about Russia freeing criminals and having them roam the streets in gangs. Or Russia forming militia out of these "animals".
Also if they are "animals", why would Ukraine release them?
An animal remains an animal, and believing there would "checks" and "safeties" in place to make sure these "animals" don't do any no-nos, especially in a time of war, is... to put it mildly... naively cute.
Want to be a national hero? How about you start by not being a criminal?