All nations change. Americans once bought and sold Africans like cattle and killed aboriginal natives for example. Which America? The one that recognized the Black man as 3/4 th of a person for representation purposes or the America of today?
If you say that is not the America of today I would agree. That is also not the Russia of today and the Chechen rebels did not start them fighting to save themselves from Russian "terror and brutality" but rather for nationalistic reasons. Using your criteria Blacks, Mexican Americans and Indians have a right to use force to break way based on past wrongs and to separate them from the Union based on ethnic or religious identity.
Since the Chechens had autonomy, and the same freedoms that all citizens of Russia had under the democratic era initiated under Yeltsin their can be no honest claim to their dispossession or loss of rights as a basis for their armed revolution.
If you are going to use past "wrongs" done to the Chechens as a basis for supporting their armed struggle then I would expect you to help the Aztlan movement bring back the Southwestern USA back to Mexico since the wrongs done to the Mexicans and Natives by the USA have been far worse then the wrongs done to the Chechens by Russia. If you can point to the mass movements of Chechens to Siberia I can point out Oklahoma and the reservation system.