When 3 million people march to "defy terror," I think it's safe to say that there will be no impact on terrorism. You don't hold political rallies to deal with a threat like that.
Let me know when 3 million people ... or even 3 people ... march in Paris over their God-given right to keep and bear arms. If they had been doing that last year, there might have been no reason to hold a rally to "defy terror" this year.