I see your point, and of course it seems wrong that it would be O.K. to say it to one group, but be punished somehow for saying it about another
group. Europe (and the world in general) is a strange place at times. Take the Roma people for instance. There is so much outright racism going on
toward the Roma in Europe, but few do anything to change it.
If anyone believes that peace on earth and the abolishment of racism is possible as long as all these different racial/cultural/religious groups
exist, they're smoking something strong. Some cultures are just too different. One may justify something that the other absolutely loathes.
It's simple. As long as one group is afraid of another they will dislike each other. As long as one group presents a threat to another, they will see
each other as enemies. It's a basic survival instinct going back millions of years.
During Hitler's time people believed that the Jews were a threat to their prosperity and a reason for why people were suffering. They were led to
believe that since the Jews owned many banks and shops, they controlled their economy. They felt that one way to take back control of their lives and
countries was to either relocate them somewhere else, or exterminate them.
During our time we've had a few terrorist attacks, all believed to be perpetrated by Muslims. Since people are afraid and have been led to believe
that the Muslim religion teaches violence against all non-Muslims, naturally they react with discrimination against that particular group. Since some
extreme Muslims have expressed that their life's mission is to spread all over the world, continue to practice their faith and slowly convert the
rest of the world to the Muslim religion (forcing the populace to live under Sharia law) it is not surprising that people are afraid of the large
influx of Muslims into their own countries. They feel that their culture, beliefs and laws are threatened by this group, and they react to it.
There's also that little thing in the Koran about Muslims being allowed to lie to the "infidels" to get their way (I could be wrong, but that is
something I've heard mentioned), so this makes it very difficult for some non-Muslims to trust the words and actions of Muslims. People are afraid of
trusting Muslims and their true intentions within their country.
Is it right to mistreat people of different religions or race based on the actions of a few? Of course not. However, human nature doesn't make it
easy not to. When we are hurt or we recognize a threat, we try to either a.) stay as far from it as possible, b.) push it away with threatening
actions, or c.) exterminate it.
I don't know how to change this in everyone. I only know what is in my own power. Maybe both groups would have to convince the other that they are
not a threat to each other, and punish those within their own groups who perpetrate hate crimes against the other group.

They have to prove to
each other that they have each other's best interest at heart. Even these actions wouldn't completely eliminate strife between different groups, but
it sure as hell would make it better.