People tend to question their nationality amongst other things when they don't get their own way. It's the frustration that is building up in people and it's spread across all spectrums where eventually no-one is innocent.
On the other side people are saying "I don't recognise my country anymore", "this is a white country", it's an identity and cultural crisis. You potentially have two types of people in America, people who remember the days when black people sat on different sections of the bus, and then people who don't just find that disgusting but feel violent protest is required to argue against anyone who agrees with it.
This is why much of the western world is on the brink of civil war, the change has been so quick and people have struggled to adapt. I agree with the changes, it is disgraceful to even consider to have black people sat in different sections on a bus but there will be older generations who honestly disagree. Then there are sections in society who aren't bothered and will argue against because it's how they were brought up and they feel the 80's or 90's was how society should be because that's how it was for them.
Here in the UK, the massive increase in migration over the last 20 years has seen some feel like we are being invaded. It has challenged peoples views, people who for 30-40 years of their lives barely saw a black person, or a Muslim. Now those people are seeing many on their streets and they feel it's an assault on their identity and their country.
I disagree with any racist view but there is a reason why all of this is happening and it's because traditional human behaviour is to oppose change and view 'unknown' people with suspect. There's no excuse for it but it's ingrained deeply in human nature and it isn't something you can just argue against or type against on Twitter.