> most important question is: who the hell decided to do such a stupid thing and in the name of what

Short answer: Russians and Germans. The former had influence in the latter. And the latter gained a measure of economic command over the continent. (With its export and energy model under shock, that influence is near its post-unification nadir right now.)

I'm glossing over anti-nuclear national politics, as well as the genuine fiscal pressure of capex-heavy power sources like nukes (versus opex-heavy ones like gas). But broadly speaking, take Russian influence in Germany out of the picture, or have one other large fiscally responsible economy going into the Eurozone crisis, and I doubt this would have happened.