Schemas, heuristics, categorization, stereotypes all are shortcuts of defining a person. They can break one down into so many little things and can be based on almost anything. Religion is one categorization, but within religion there are sub-sects and within those there are other sub-sects. And from herein comes a superiority complex of who is right and who is wrong.

This complex exists within Muslims regarding their own religion. A constant state of how I practise is correct and everything else is just wrong. And yes, sometimes some methods of practising can be wrong and have no religious basis. But, most times there are some grounds to a practise even though it may not be followed by you.  Learn and respect these differences. And above all don’t ever call a believer a disbeliever; that is for their lord to decide.

Abu Dharr is reported as saying that he heard the Prophet, may Allah bless him and grant him peace, say, "If a man accuses another man of deviance or accuses him of disbelief, that accusation will come back on him if his companion is not as he said."
[Al-Adab-Al-Mufrid - Imam Bukhari]