We hear about it all the time. It's just so pervasive we no longer see how extreme is the intrusion!
Civil asset forfeiture, stop & frisk, the near endless litany of TSA/Homeland Security abuses, "VIPER" teams hassling Greyhound bus riders, states such as Hawaii where the 2nd Amendment is ignored, the SWAT teams that have taken over every small-town police department, the banking secrecy acts that report you if you move more than $4000 at a time or in an undefined "suspicious" way (also see "structuring"), the aggressive+confrontational transformation of law enforcement into domestic military, the involvement of military at WACO... need I continue?
The fear, of course, is such restrictions would be next. You start by going after the boogeymen, terrorists and pedophiles, then expand to gangs, then drug dealers, then political enemies, then....
[1] https://ucr.fbi.gov/crime-in-the-u.s/2013/crime-in-the-u.s.-...
[2] https://ucr.fbi.gov/crime-in-the-u.s/2013/crime-in-the-u.s.-...
[3] http://edition.cnn.com/2016/10/03/us/terrorism-gun-violence/
Anecdote: I live in one of the lowest crime neighborhoods in Chicago. Every now and again though someone is shot in the area. The first thing I always wonder: was it random or was it gang/drug related? Nine of ten times it's the latter and I feel better because I don't associate with gangs or regularly participate in drug deals in a McDonald's parking lot at 4AM. It's scary when it's random because it's easy to think, "that could have been me, it could have been anyone."
That's why terrorism is scary (and that's why the terrorists do what they do). Of course protections should be in place, but there's simply only so much you can do before you're policing every aspect of everyone's life to prevent the tiniest chance that something happens to a tiny percentage of people. But, damn, is it scary.