Keeping track of, and denying reentry into the country for all jihadists would be a start. Right now we're mostly guesstimating how many of our own (so-called) citizens are, or have been, fighting as non-regulars in Africa or the Middle East. If three veterans already on watchlists could cause this much damage in France, imagine what the hundreds of unaccounted for veterans can do.
Another would be to deny Saudi Arabian investments in mosque buildings across Europe.
By the way, who says you need laws restricting free speech, in order to restrict free speech? Right now the attitude in Europe is:
"You have a legal right to say and write what you want, but people may try to kill you for it, and we won't take any steps to guarantee your safety."
You don't think this makes people think twice before speaking their mind?