"A surprising thing about the US (I've seen reports from the deep middle west) is that the more liberal part of the country lives either in big cities, the west or the east coasts , or abroad, and they are the most at risk from terrorist attacks, while the most conservatives, the most security obsessed live so deep inside the country, they don't run the risk of interesting foreign terrorists."

Even in a full scale nuclear exchange between the Soviets and US the planet was not going to literally "blow apart". You are probably "at best" you were looking at a 50% kill rate- everyone knows that after affects of a full scale nuclear exchange would probably kill more people than the direct effect of the nuclear explosions.
The problem with major terrorist attacks is that they will change politics. If New York gets hit nuclear weapon, how will Americans respond. Or if Paris is hit with a nuclear weapon how will Americans respond. The actual chance from dying from such a attack even if you live in a city is pretty darn low, but everyone including a goat herder in Tibet will probably be affected by the "after shocks".
The result of a major terrorist attacks will probably mean Americans will no longer have much patience- diplomats might be replaced with simple ultimatums. Threatening to reduce Iran or N Korea to a glass slag wasteland becomes thinkable. Few people should wonder whether this will produce results. But if even it "works", it will be a massive failure.
America of course isn't the only country on the planet, how will the Russians respond? If you threaten to use nuclear weapons, you better be prepared to use them. If you use them, when do you stop using them? The Russians have thousands of nukes. Look at a very simple use of these weapons, say the Russian simply decide to sell them to highest bidder. A nuclear weapon system is cheap at a price tag of a billion dollars, so a 1000 nukes is trillion dollar- it makes the Russians rich before the world dissolves into madness.
If nukes are used, then more countries are going to make them and more countries are going to use them- there currently tens of thousands of nukes, it's possible before we all are dead that hundreds of thousands of nukes could be made.
Now a nuclear weapon is the best sharpen stick, but we of course have more kinds of weapons of madness- biological weapons aren't a very good weapon unless you simply want to infict the most amount of "pain", so of course these would be used.
Wars don't usually kill that many people- diseases have killed far more than all the wars that humans have been involved in. But with modern weapons this could change with modern weapons human extinction is possible.