Google is resisting the government's intrusion, not to protect our privacy, but to further their own ends. As it happens, these two goals coincide. The moment Google perceives an advantage in working with the government, you can count on our privacy being violated.
I think that other search engines already capitulated. IIRC, Yahoo! and MSN gave up without so much as a sqawk.
I doubt it would be dangerous to research how to build a nuke. This information has been public knowledge for decades, as one high school kid showed in a science project where he developed plans for a nuclear device. This was before the Internet had become so popular. Remember, too, that there is all sorts of public Internet access, such as libraries or Internet cafes. Anyone who was up to no good (and who had a lick of sense) would seek such anonymous access. The possible benefit of "security" is an illusion; the known risk of invasion of privacy is almost certain.
Claiming "National Security" is often nothing more than a ploy to invade privacy and dig up dirt on people the authorities don't like - people who may be agitating for legitimate change, but who are causing the administration too much trouble. Look at all the politicians and others who have been forced to step down or to shut up, because some irrelevant and ancient information had been dug up about them. Someone smoked a joint in the 'Seventies, and is now considered unqualified for some position. Or they had an affair, or otherwise did something we don't approve of, facts dug up only to smear them, and not because these things have any bearing on their present capabilities.