We can blame Carter for not allowing the Iranian military to crush the clerics in 1979-1980. They were itching to do it, but our moralist in chief refused to support this. Had they done it, we probably would have gotten a military-ruled Iran for a few years, and then a return to civilian rule, a la Turkey. More importantly, a key Middle Eastern state would have remained pro-American and the terrorists in Lebanon and elsewhere would have been deprived of a major funding and arms source...
you're assuming that the harsh crackdown would have worked like a charm, the fact is there is no way of knowing how things would have turned out in the event that carter let the Shah take off the gloves. Half the Iranian army could have mutinied at the thought of massacring hundreds or even thousands of their own country men, the situation could have degenerated into a bloody mess. then you could get the Russians supplying the opposition with weapons of their own then maybe even Saddam decides to take advantage of the situation. Hell things may very well have turned out the same as in OTL. The fact is that a violent crackdown against the revolutionaries was a morally reprihensible act, one which has no guaranteed outcome. The one thing we do know is that when the US sticks its nose in the internal politics of other countries, the track record is mixed at best.
You blame carter for Iran being the nation it is today, but what you fail to realize is that it has gotten this way after decades and decades of history, with lots of events which transpired long before Jimmy Carter was even sworn into office. Hell foreign intervention in iran is one of the main reasons why the Iranian government is so hostile to western nations. I'm not saying that if Carter let the Shah crack down on the demonstrators that the world wouldn't be a better place today, but there is no way to know that, and giving him all of the credit or blame for the way any situation turned out is crazy.