"How Twitter Is Messing With Al-Qaeda's Careful PR Machine."

"Individual jihadis are increasingly taking to social media with their own opinions, sparking disputes within the terrorist organization."

It's a marketplace of ideas. As Justice Holmes famously said:

If you have no doubt of your premises or your power, and want a certain result with all your heart, you naturally express your wishes in law, and sweep away all opposition.... But when men have realized that time has upset many fighting faiths, they may come to believe even more than they believe the very foundations of their own conduct that the ultimate good desired is better reached by free trade in ideas — that the best test of truth is the power of the thought to get itself accepted in the competition of the market, and that truth is the only ground upon which their wishes safely can be carried out.

Good luck shopping.