"Law enforcement" has no job until a crime has been committed. There is no point in attempting to foil a terrorist plot that doesn't even exist. We could do without all of this pre-crime BS.
The FBI can't prevent terrorism. That's not how terrorism works. Any idiot can kill a bunch of random people on the street and there is literally nothing you can do about it. And notwithstanding that, it still doesn't happen often enough to be worth spending half the resources on it that we do.
But the real issue in this context is that the people in charge of the pre-crime BS are the same people in charge of putting you in prison for violating the law. Such people are extremely dangerous to normal people because they can so easily ruin your life with a pencil, which is why good upstanding citizens legitimately take such exception to encountering them in these types of situations.
It's the chilling effects problem. If something like taking pictures of things causes a visit from LEOs then you're liable to stop taking pictures of things, or advancing your political views in public, or associating with certain people. Which is a totally unacceptable reaction for LEOs to be causing in upstanding citizens who are doing nothing wrong.