That's an unfair double standard Always.   The most religious place I've lived was Pella, Iowa, almost 50% of the citizens attended church every week.  As an example they started with a single Reformed church, but now have 2nd and 3rd reform churches that emphasized different directions in their ministry and definitely included different interpretation of the bible and its intent.

Your belief that there is only one real Christian church theology is a lie.  The arrogance of that lie is not unusual, I've seen Christian churches that expel member for breaking that church's 'rules,'  (who find other Christian churches by the way),  Fundamentalist Islam is closest to what you seem to be saying.   The believe only strict adherence to their form of Islam will bring salvation.  The kill other Muslims because of this conceit.

When you tell others that their faith life means they are going to hell what are you telling them at the emotional level?  

Who makes judgements on those of faith?