Basically, people who are stupid enough to follow a religion, think other people stupid enough to follow a different religion are stupid and wrong and that giving them a good short sharp shock like killing them will teach them not to be wrong anymore.
Governments who feel that this gives the morons a right to religious freedom and legislate in favour of that ideal tend to find religious cretins use that freedom to kill even more of each other.

Maybe religious intolerance is evolution's way of purifying the gene pool of bloody fools, if enough of them kill one another one day there will be atheists left to breed with one another?

I am not sure how Pew defines "social hostilities involving religion?" Is this society supporting religious activities or against? I cannot find the Pew study mentioned in the article.

All the more reason to have no religion., a pox on all of them I say. Not one person can prove any of the religions they swear by as true really exist and yet they are prepared to kill if necessary for that fiction. Muslims kill to protect the honour of their prophet and discriminate against Christians and others. Christians call Muslims barbaric murderers and terrorists and Hindus and Buddhists practice genocide against minorities. This world would be much better if we could stop focussing on our differences and acknowledge that we are all the same under the skin. Religion only complicates this even further.

It seems we're becoming less tolerant as the population increases; normal animal behaviour really. The most aggressive tend to rise to the top too, so that's something fun to look forwards to.