Crimea is currently populated by 70% ethnic Russians, who have been the majority for at least 50 years, and the plurality for at least 120 years. The reason it became part of Ukraine is because the USSR transferred it there from Russia in 1954.

The only benefit to Europe and the US of complaining about the annexation is to put pressure on Russia. Nobody wants the ethnic cleansing that would occur if Russia actually retreated from Crimea (and any Russian politician, dictator or not, who allowed that to happen would lose their political career and maybe their life.) If it weren't for the horrifying virulence of Ukrainian nationalism, I'm sure a lot of the ethnically Russian residents would be glad to be separate from Russia.

Do you seriously think that if the residents of Crimea freely voted, they would vote for a Russian retreat?