Tech that enables education, work training, and cultural assimilation for disenfranchised minority youths is frowned upon in civil liberties circles?

You demonstrate the colonialist mindset that doesn't understand other cultures seek other ideals than your own. Were the 9/11 hijackers "disenfranchised minority youths"?

Doesn't France have social systems to enable the first 2, and the 3rd is up to the person.

These people aren't victims. They made a choice.

So why didn't the NSA report this suspicious activity to the French authorities?

Who said they haven't and who said such acts weren't foiled by intelligence agencies before?

Well if they have reported it, why did it still happen? You are asking me to prove that the NSA hasn't foiled any attacks instead of asking the agency conducting mass surveillance to provide evidence? Just to give you an idea most terrorist attacks on US soil, foiled or not, have been directed by the FBI. Source is The Intercept.

Tech useful for surviving it might be more our thing, though...

There's also a comparatively low-tech piece of engineering we law abiding Europeans don't have access to that may help individual citizens in cases like these.

surveillance is not a solution to the problem it merely suppresses it.

Treating symptoms is never as useful as treating the underlying cause.

We're lacking the tools to deal with this problem. All we can do is try and contain it.

The containment is driving the feedback loop thereby keeping us from improving the situation. We need to take a leap of faith in order to break it.

Like others have said the damage this is causing is mostly mental. The number of random (I mean that as in could happen to anyone not downplaying the significance of human life) deaths caused by terrorism is not so large.

However this does not mean we should tolerate people who refuse to play by the rules of society because of their personal beliefs (whatever they may be). Any countermeasures must be above board and transparently fair.