One of these things is not like the other. Russia is a threat to Europe, and is in the midst of invading a country with a lot of agricultural, industrial, and cultural upside that should be on the road to EU integration. Bombing the snot out of Russian trenches in eastern Ukraine might even be a good idea.
And the reasons for bombing Iran are...?
Perhaps letting Iran, a country ruled by fanatics, build military infrastructure enough to be able to hold a significant part of the world's energy hostage was the original blunder?
You could argue they'd never use their power unless attacked, but I don't think you can be certain of that. It comes down to if you can accept that a non-rational actor can be allowed to have this power (or nuclear weapons for that matter).