The people of the Crimea ultimately should be given the right to self-determination, so if a fair and open referendum is actually going to be held then it's really the only way to go.
Who are "the people of the Crimea"?
It could be argued that "the people of the Crimea" are the Crimean Tatars. Stalin forcibly displaced or killed them and replaced them with Russians, but the Crimea was Tatar land for ages. There are plenty of them in other parts of the world, including some who were born in the Crimea and got out before Stalin's persecution.
But how far do you go back? The Crimean Tatars got the Crimea in the same sort of way, maybe even bloodier. Is their claim really better than the Russian claim?