"Latvia is a nation, and Latvia must be for the Latvians. If those Russian ethnics want to be Russian, then they are free to vacate Latvia and emigrate back to Russia"

Ethnic cleansing is the only solution? So those from Russian ethnicity who have been born in Latvia for at least three generations should leave the country? 
Here in Canada newcomers and established communities alike are free to speak their language and keep their food and culture alive. It's called multiculturalism. Ask the Ukrainians in the Prairies and the Chinese in Toronto, etc. if they would like to be expelled to the 'old country'.