The failures of introspection

about a hundred years after the muslims of spain decided to become introspective, to purify their faith, there were no muslims left there.

A few centuries after the muslims in the middle east followed the same pattern, it leads to where we are now, through many bloody periods where people such as ibn wahaab took the purification to such degrees that they considered it not only halaal, but their duty to shed the blood of other muslims who had a different Aqeedah (they considered them mushrik).

So why is it that muslim scholars find this instropection by muslims to be such a beautiful thing?