It is isolated conflict that should be solved between countries involved.
If Russia is selling gas (anything) cheaper you should just buy it as it serves citizens of your country.
Throwing nuclear is a mistake but it has nothing to do with Russia.
My arguments are:
Russia has "Imperial ambitions" towards Ukraine, Georgia, Baltics and etc. Putin is stating that collapse of Soviet Union was the biggest mistake ever, all the internal communications in Russia are very aggressive, Putin was threatening nuclear weapons in the beginning of the war and etc. Medvedev is on another level threatening everybody around - see my previous comment for example.
This is where geography becomes important. While conflict is in Ukraine now, a lot of people believe that it might spread.
Why? Because Russia is influencing EU politics, using soft-power, social media to influence opinions and etc. Russia is very much involved for a long time already. It is not like German addiction to Russian gas was not influenced by Russia. Russia has further ambitions, always had. Russia is not just calmly existing inside of its territory. It always had global agendas. Like any other country.
Values. In the end Europeans have some values and most importantly EU is built on some fundamental values. Democracy, human rights and etc. Authoritarian country starting land wars in the Europe and threatening others does not sit right with it.
I can't agree that "most people in Eastern Europe have a very hard life already". Define "most" and "very hard life". It just means nothing. The thinking is that being at war is on another level "very hard".
So keeping in mind these it looks natural for EU to get involved. Because there is a belief in values and a belief that if Russia is not stopped, conflict can roll over to further countries. A lot of rhetoric from Russia actually state it.