Crimea, Luhansk, and Donetsk are not Russia, and never have been, they are Ukrainian territories that have been illegally occupied by Russia. If there is people that wants to be Russian in those territories, they should go and live in Russia, not Ukraine.
Otherwise, tomorrow Putin can go and occupy Kyiv just for the time he needs to deport most Ukrainians living there, and put an equivalent number of Russian citizens in their place, then make another quick referendum and voila’ Kyiv is now Russian.
No way.