Alain de Botton wrote about Michel de Montaigne, a XVI century philosopher from Gascogne, who had first pointed out that a society's definition of normality was constrained by its own experience, customs and practices.
In 1580 Montaigne went on a 3,000 mile journey on horseback travelling from his home in south-western France to Rome via Germany, Austria and Switzerland. It was his first trip outside France, and he observed local customs in every place he and his companions visited. He also observed that his companions were getting upset by the differences they encountered whilst on the road: they complained about unfamiliar food, uncomfortable beds, incomprehensible language foreigners spoke. "Wherever they go they cling to their ways and curse foreign ones" - wrote Montaigne later.
Back in France, Montaigne became interested in the chronicles of the exploration of South America. He was fascinated to read about American tribes in which virgins openly displayed their private parts, men were allowed to marry each other and spiders were considered a delicacy. He was saddened to hear that Portuguese and Spanish conquistadores had decided the native Americans were barbarians, wild beasts to be enslaved or murdered. In just 50 years the colonists have reportedly reduced the indigenous population of South America from 80 million to 10 million. "Each nation has many customs and practices which are not only unknown to another nation but barbarous and a cause of wonder", wrote Montaigne. The native Americans died because their customs did not match the European standards of "normality" of the XVI century.
As I was reading de Botton's musings, I thought about the currently well publicised open homophobia in Russia. It is sad to see that some people are so stuck in their narrow-mindedness of what's "normal" that they feel justified in their groundless aggression towards homosexuals.
I toyed with some extreme examples here but I merely wanted to open your mind a little wider.
P.S. Next time you go to France, have a frog.