Hate to break it to you but just because a majority of Crimea are ethnic Russian still doesn't mean they want to be part of Russia. 58% are ethnic Russians but many of those still identify themselves as being of Ukrainian nationality despite their ethnic origin.
If the referendum was free and fair it's almost certainly the case that Crimea would not vote to be part of Russia, in fact, a poll was done on exactly this before this shit even kicked off as it has now:
Even in Crimea, the most Russian leaning part of Ukraine support for joining Russia was at only 41% - not enough to win a referendum.
If you can't see why Russia has shut down movement in and out of Crimea, if you can't see why it's denying access to international observers, if you can't see why it has plastered billboards in pro-Russian propaganda and seized radio and TV transmitters, and if you can't see why it installed a pro-Russian administration in Crimea kicking out the previously democratically elected one then I probably can't help you understand what's going on here, but I figure it's worth trying. Russia is annexing Crimea, not because the people there want it but because Putin both wants it and wants to send a message to any other nation considering breaking away from his control that it wont be painless.
If the people of Crimea genuinely wanted to break away from the Ukraine do you not think a referendum with international observers would be sufficient? Why the propaganda campaign? why the hijacking of TV and radio to shut out information from the rest of the country? why the presence of Russian troops and the isolation of Ukrainian military to their bases so they can't communicate with the populace? Why is all this necessary if Crimeans would vote yes for independence anyway?
Russia has been playing a game in Ukraine for some time that would make even the CIA look like amateurs - even during the protests we had protesters being dragged off by kidnappings that could only be the work of state-sponsored organisation and beaten and left in the forest to die with one or two surviving against the odds to state that the people who did it spoke with actual Russian accents (yes, you've got it, Russia had death squads in the Ukraine during the protests). You had eyewitness accounts from both protesters and the police that snipers were shooting at both police AND protesters to try and provoke a bigger confrontation between the two.
So wake up and smell the coffee, Russia has been playing games for years in the Ukraine, those games are finally just coming to the light and there's no way the referendum on joining Russia can be considered the slightest bit free and fair whilst Russian troops and propaganda are controlling every bit of information in and out of the territory right now. Even if the people made up their own mind, how would you possibly prove the Russian troops aren't just changing the ballots? with no international observers confirming the fairness and legitimacy of the vote you might as well just make up the results right now and have done with it - it'll be no more or no less legitimate.
If the Democrats sent the military into Texas and blocked all communication and access in and out, took over the TV and radio transmitters there and plastered Democrat propaganda on every billboard whilst making up things about the Republicans, beat up pro-Republican journalists and so forth and then went on to win Texas with a landslide would you really, genuinely call that an acceptable outcome? a fair election? a legitimate election? That's exactly what's happening in Crimea.