Because a first strike would involve more than a bunch of GI's on the border. It would have to be a concerted bombing/insertion campaign whereby Iran's array of nuclear development sites could be captured/destroyed. This isn't Osirak. They're spread out across Iran. And much of it is reportedly underground. Not even Israel can admit they have the capability of repeating what they did at Osirak.
So tell me again how we're going to pull off an effective first strike in Iran unless it involves the nuclear option?
A first strike has to be the last strike, if Iran achieves critical nuclear mass (if it hasn't already). It would have to be a decapitation of leadership, and all those attached to the decision makers in their military.
"Because a first strike would involve more than a bunch of GI's on the border. It would have to be a concerted bombing/insertion campaign whereby Iran's array of nuclear development sites could be captured/destroyed."
And a concerted bombing/insertion campaign would be impossible unless we had based right next door in Afghanistan and Iraq.
I'm playing devil's advocate with you here, and I honestly still do not understand how you wouldn't draw the opposite conclusion based on the reasoning that you've given so far.