If Russia thinks it belongs to them they should try to take it. If they want to act like victors in a war over conquered neighbors, then they should defeat them first.
They've done it once. They could very easily do it again.
What you're arguing is that might makes right. Actually, it doesn't.
These people in Latvia didn't ask to be there; they were born of Russians forcibly relocated there by Stalin, or the descendants of same. They didn't ask for their lot in life. Punishing them for the sins of their grandfathers' and great-grandfathers' rulers fits no definition of justice that I can comprehend.
If you think that denying them citizenship based solely on their ethnicity is a good thing, then you're arguing that rights are, in the end, completely alienable and subject to the whim of the majority.
I'd love to hear you argue that vision with the same intensity when you're in the minority.