Why is the world becoming so intolerant to others who are different?

I doubt it's any more or less intolerant than was always the case, but the rise of systems like the Internet and the major [anti]social companies has made intolerance and fear of "difference" easer to see, to encourage, to propagate.

A major case study is Extraodinary Popular Delusions and the Madness of Crowds, by the historian and journalist Charles MacKay. It should be required reading for what it still teaches about mass- fear and intolerance, using examples from Mediaeval to his own time ... the middle of the 19th Century!