Islam is a religion of peace... except when it isn't.
Christianity is another religion of peace... except when it isn't. Hitler went through catechism classes, and maybe so did Mussolini.
Most religions consider themselves to be the one true religion and superior to all the others.
What is certain, from a logical standpoint, is that one of them is the One True Religion... or none is. Maybe there is no one true religion, perhaps it hasn't been invented yet, in the same way that gravity or the atmosphere was unrecognized for centuries.
Juniorbush does nor want to irritate his Saudi pals by saying that Islam is NOT a 'religion of peace'. Most Muslims are peaceful most of the time, after all. as are most Christians, Buddhists, Hindus, T'aoists, Shintoes, Jains, Bahai'is and Sikhs. No religion wants to be known as a terrorist cult, of course.
McCain should do whatever tickles his fancy. If he continues using the term 'Islamic Terrorists", there are many who will not vote for him, and no doubt many who will.
The 'truth' is not the important thing in a campaign. Votes are pretty much everything.