Unnecessarily hostile? No. People who have to constantly deal with a difficulty other people don't have, while those people completely unoriginally reflect the same doubt that's been repeated over and over again, can make frustrated comments in a thread on the topic without being characterized as hostile.

It is a calmly stated ignorant opinion.

Imagine living with a diabetes, or some other invisible issue that affects your life, and having to hear such calm opinions all the time from people around you. Telling you that your issue is not real (so - de facto - you're imagining it).