Everyone who think there should be consequences for Russia for doing this. Why? Whats the point of escalating the situation? Russia has only taken control over parts of Ukraine that were practically theirs already. As long as there is no real threat of further aggression from Russia, for which Ive seen 0 good arguments, "punishing" Russia with sanctions such as stopping gas trade is outright silly and will only hurt everyone in the long run.
If Russia takes Crimea by force (and putting troops in Crimea for intimidation is force) this month with no response, what's to stop it from taking Donbas or Kharkiv? Perhaps they want to protect the ethnic Russian population in Latvia from the West? Putin's goal is to restore Russia's influence in Eastern Europe for the sake of prestige. He was incredibly embarrassed to watch the former Soviet satellites break away and largely leave Russia's sphere of influence in the 90s under Yeltsin. He's spoken about it before publicly and it plays well with the public who are eager for a return of some of the country's status.
After Ukraine began to trend towards the West in the last decade, Putin, via Yanukovich/PR, halted Ukraine's dialogue with both the EU and NATO while increasing the country's dependence on Russia for subsidies. Russia, in return for its investment and money sent to eastern Ukraine expects patronage from the people there and is getting it, unsurprisingly. After Russia has moved into Crimea with its military or mercenaries, there is no way any referendum can be considered legitimate. Look at what Russia does to its own citizens who speak out or protest against Putin, including journalists. They either end up in prison or dead. Alexei Navalny was yesterday put on house arrest for two months and banned from the internet or telephone to remove his most prominent critic from public life. Protestors from his inauguration were sentenced to 2-4 years in prison shortly after the Olympics ended, which conveniently avoided any international criticism because of the timing.
Do you think that anyone is going to come out and defy the Russian military that is in Crimea? The Tatars, Jews, Ukrainians, and others aren't going to vote no in the face of coercion. Meanwhile, when the referendum results come in and it is overwhelmingly pro-Russian, Putin gets to celebrate his perfectly executed democracy.
In 2008, it was "oh, it's only some small, backwater regions in the Caucasus." Now: "It's just Abkhazia, South Ossetia, and Crimea. Russia won't try to expand anywhere else."