I can relate to your annoyance, but even in a grander scale when folks criticize another's religion without a comprehensive understanding of the structure of said religion.
But I certainly can appreciate the frustration when people that are supposedly of the same worldview criticize one another.
On either scale, I struggle to wrap my head around why people, being of one commonality, are so quick to choose to be critical rather than understanding.
Yes it's tough some days. I'm guilty as well. But in Hinduism, even the so called universalist leaning sects or sampradayas are also sects unto themselves. It's an irony that is sometimes missed. For me perhaps it boils down to the difference between saying, 'I'm right,' versus 'My views are different than yours."