وَإِذَا قَرَأْتَ الْقُرْآنَ جَعَلْنَا بَيْنَكَ وَبَيْنَ الَّذِينَ لَا يُؤْمِنُونَ بِالْآخِرَةِ حِجَابًا مَّسْتُورًا 
It is safe to say that a given religion can be judged correctly only by two things: its own teachings and the practice of the mainstream doctrine of this religion. A religion cannot be judged by the centrifugal practices or beliefs of some followers, be they liberal or extremist, hither or thither.