Most people seem to be mentioning why terrorists won't be using facebook and instead some more secure etc.
That's probably not the issue FB is countering. They are/should be focussed on the content that's spreading radicalization/extremism. Lots of pages do that and since so many people have access someone is bound to be attracted!
Just recently a young female doctor from Pakistan was in news becausr she joined a terrorists group because she liked there posts/propaganda videos on FB. Thankfully she was caught during a operation!
Thag content really needs to be controlled! It's making small groups being a able to raise money/attract followers quite easily with just a private fb group or page!!