Couple of points.
On what to do about radicalization of Muslim youth, so far the most succesful model seems to be
the Aarhus model. (AKA "the hug a terrorist model").
The Aarhus model is about as stereotypically left wing approach as you can get.
In comparison, the popular right wing approach of increased surveillance, limitations to the human righs of Muslims (for example controlling how they can dress) and harder police measures have proven to only increase the problems.
You see, I don't give a flying ficus about any of the talking heads posted in this thread. Left or right, they're mostly just collecting speaker fees, selling books and generally attention whoring. What matters are the actual policies put in place, and the results they bring.
People are way too concerned with what they feel, and way too concerned about "is this right or wrong" and "who makes the better arguments". ISIS is not a hypothetical. What matters is what works. "Hug a terrorist" works. Right wing policies don't work.
More generally on the term "regressive left", it's your stereotypical weak man fallacy. It's picking the most radical and/or terrible proponents, and claiming they represent the whole.
It also always seems to be a kind "No True Scotsman" in reverse. If you're a moderate, reasonable left winger, you're no real leftie.