Yeah they can get it from elsewhere, but that doesn't change the fact that Europe gets a majority of their oil/gas from Russia right now and it's their preference to do so.
If it were so easy to just make the switch then why haven't sanctions been implemented yet? Why are European nations divided on the subject? That's why its a lot of talk rather than action, that's why Europe wants dialogue first which Putin and the Russians were expecting. Plus alternative energy isn't gonna work in Germany's huge industrial sector for example. Just as you say the citizens chose, the citizens also voted in elections for Yanukovich. There was no objections to the elections by the international community, so why should the people that voted for Yanu suddenly have no say? I'm not saying Yanukovich was worth a shyt he robbed the treasury blind, but we can't act like opposition figures like Yulia Tymoshenko haven't been corrupt individuals in the past either. Just think about how this looks, a democratically elected head of state(albeit a dirtbag) is chased outta town by a band of protesters, hooligans, and extremist neo-Nazis, rather than holding new elections and respecting the democratic process of the country and building unity through a new coalition govt represented on all sides.
Truth is, the EU started this conflict and rather than agree on some middle ground between East and West they accepted a hostile undemocratic takeover and then chastised Russia for not respecting the rights of what they view to be an illegitimate regime. It'd be one thing if the whole country was pissed, but it's obvious the anger was mostly from the Europe leaning West of the country, the same side that lost the elections prior. Nobody is innocent in this.