Open Question: Is it a mistake to leave Iran unchecked?

like it or not we are in a global competition for power and resources. The human race always has been. It is not a safe world, the lessions of history have taught us this. We would clearly be better off if Irans gov was not so extreme. But will they pose a big enough threat to us in the future that we should take action now? An iranian superpower would be a nightmare for the united states I dont think anyone would argue that. But does it seem likely that if left unchecked they would gain this much power? or is it possible we can coexist with them in peace?