The problem is that Iran will kick the ass of the American army.
That's probably the most ignorant thing I've ever heard.
As for why we should have gone into Iran in 1979. When the Islamists took over and seized the US embassy, that was the first "terror" attack as we know it today. Instead of waiting around for over a year, and trying pathetic rescue attempts which ended up in deaths by incompetence, we should have invaded. I'm pretty sure seizing an embassy and holding hostage its occupants is a clear act of war. By stamping out that "terrorist" act, it would have sent a loud and clear message that those tactics would not work. Instead, we allowed them to see that "oh...if we use these tactics, the US won't do anything about it!" What do you think they're going to do in the future? The same thing. Iran was the begining, and it should be the end of the huge problems in the Middle East today.
This state run by Islamists, who openly profess to hating the West, to starting up their Nuclear programs, and who are willing to sell their weapons secrets to the highest bidder, amongst a plethora of other things, clearly poses the greatest threat to regional and international security. North Korea doesn't even come close. The British already know this, and have been recently trying to publically prove the Iranian presence in Iraq, in order to start the domestic campaign of winning over support for action in Iran. The fact is that Iranian soldiers have been aiding the Iraqi insurgency and have been carrying out attacks against Coalition forces. We find men all the time who are wearing nothing but their underwear, standing next to an Iranian military uniform. When asked about it, they say "oh its not mine." Sure. OK.
We will, no doubt, have a much harder time if action was taken in Iran than in Iraq. Iran's technology is far superior, and they're military much more advanced than Iraq. They still have working AA guns positioned everywhere. States like Russia and Taiwan still trade arms with them. It won't be a walk in the park to Tehran like it was to Baghdad. But guess what....if we go into Iran, we'll actually fight a war. Not a backyard scuffle like in Iraq. The US, and the HUGE coalition that would without a doubt come with them (I can't see anything but multilateral participation through the UN on this one, especially now with the nuclear posturing on the part of Iran) will wage a real, total war. None of this 50,000 troops and lots of technology shit that Rumsfeld fucked up on for Iraq. No. Minimum 500,000 troops in the coalition. Total war must be waged. Stamp out any resistance. That way, there can be no insurgency. If we actually fought a real war in Iraq, there would be no insurgency now. Send a crapload of troops in now, and you won't have the problems like that later on down the road. The reason people seem to underestimate the American military is because we haven't actually fought a war since World War II. Korea, Vietnam, Iraq both times, all the little conflicts in between. Ask a soldier, especially from Vietnam, and they'll say "they wouldn't let us fight." Hell, in Vietnam, every single little military action had to be approved by LBJ! "Uhh...President Johnson, this is Charlie company. Can we attack this enemy position across the road?" "Umm.....lemme check. I'll get back to you." That's pretty much how it went. The difference will be that a real war will be fought in Iran, the groundwork is already being laid. Real, total war is going to be waged. And it's going to be hell. War is hell, as the saying goes, and it has to be hell. Because if it wasn't, people would fight them all the time. Iran needs to realize that they can no longer afford to counter the world powers.