If a violent criminal tried to break into my house, I would definitely not try to fight them alone. I do not have a death wish.

Of course Russia should not occupy Ukraine (and neither should Ukraine act as an occupying army towards its own Russian minority). But questions of what is right and what is wrong will not be decided on the battlefield. The only thing that will be proven on the battlefield is which side has a bigger army, and we already know the answer to that question.