It doesn’t matter that the referendum did not allow voters to express a preference for the status quo, that many of the 90+ percent who favor annexation by Russia (according to (possibly questionable) exit polls) may have been trucked in, that international election monitors were not used, that ballot boxes may have been stuffed, that Tatar groups refused to participate, that the public debate was drowned out by pro-Russian propaganda, and that Russian soldiers and/or pro-Russia militias roamed the streets. It is sufficient that there wasn’t violence, that western journalists were free to move about and interviewed plenty of ordinary people who strongly favored annexation, that there were enthusiastic public demonstrations in favor of annexation and celebrations after the result was announced, and that the outcome is consistent with demographic realities and what seems plausibly (to us ill-informed westerners) the preference of most Crimeans. Unless large groups of Tatars and ethnic Ukrainians take to the streets to protest the referendum and are clubbed by riot police, any western effort at this point to try to rescue Crimea from the invaders it embraces will be not only pointless but ludicrous. The West is now in the impossible position of being pro-democracy and arguing that Crimea should be returned to Ukraine against the will of the people. Even if the referendum was all theater, it was effective theater.
The image above, from Wikipedia, shows the demographic composition of Ukraine as of 2001. Blue means an area where the majority speaks Ukrainian; red means an area where the majority speaks Russian. Doesn’t this suggest a forgone conclusion once Putin made his move?