Who's to say what following a religion well actually means? Doesn't nearly everyone believe they're doing what their god wants?
They might believe it, Eraser, but while subjective, there is still some fact checking that can be done. Religion is not just about belief, and tools like reason and logic can (and should) be brought to bear.
For example, if Christians are killing others in the name of Christ, does this square with "Love your neighbor as yourself"?
If Muslims kill someone for converting away from Islam, does this square with "Let there be no compulsion in religion"?
I suggest in instances like that, it's pretty clear that people engaged in such acts are actually not following their religion well.
Would you disagree?