If Iran is going to do, or is already doing, cyberwarfare then they'll do it whether or not they get attacked first.
Why? Is that because you assume that Iranians are irrational and evil?
Usually people do stuff because it benefits them somehow. So, why exactly would Iran launch a cyberwarfare attack against the US in a world where the US didn't strike first?
But now, everyone will be on guard.
Given how completely we've failed at building secure systems, I'm not sure that really helps.