Now that I've got you informed, let's talk about this event. What happened, although people die everyday from anything as big as bombings to suicides, was horrific. I mean can you imagine enjoying a concert you were anticipating for weeks, expecting to be safe just to watch people die a couple feet from you. Not only should we mourn the dead, we should be there for those that survived, those who had to experience things you only see in movies or in the news from 3rd-world countries.
Not too long after the attack itself, ISIS took responsibility for the attacks. They described it as revenge on the people of Paris for doing things like insulting the profit Mohammed, attack strikes on Syria and other possibly offensive media. Now some people, once realizing that ISIS was behind the attacks, decided to directly blame to Muslims in general and in my opinion, that's exactly what ISIS wants.
Think about it this way: ISIS wants people to join their cause right? Well what better way to recruit people than to make the rest of the world hate them so that they have nowhere to go except to them. Which is clearly happening to people attacking Muslims on social media, in the streets, etc. If ISIS can get people in the 1st world to begin despising all Muslims, then they get your support in attacking those who they believe are full of sin.