There were no citizens of Latvia until 1990. When Latvia obtained its independence, the equitable thing to do would have been to grant blanket citizenship to any citizen of the former USSR then living within Latvia's borders.
Basing citizenship on some racial or ethnic standards is distasteful, to say the least.
The Soviets settled Russians there to destroy the Latvian culture just as you said. Now their genocidal "diverse" empire is over and its time for them to take their "anchor babies" and go home where their true loyalties lie if they refuse to assimilate.
This is exactly what the minorities were promised if they would vote for independence. Of course they were back stabbed ASAP after independence. Interesting that all those Latvians living in Russia, and Lithuanians, Estonians, etc, are not denied their Russian citizenship. Nor the million Georgians who migrated to Russia in the past 13 years (note the majority of these guys were the ones protesting for independence. As soon as they figured out what an economic mess they made for themselves they abandoned ship.)