It's allowed in the sense that people are allowed to be wrong and/or ignorant because that's what most of us are on most topics. We can't stop that any more than King Canute could stop the waves. The important question is, what's the best way to handle it if we want to have an internet forum that doesn't suck? Experience teaches that the answer is: the patient supply of correct information by people who do know about a topic.
I don't mean to minimize how infuriating it is to be surrounded by a flood of ignorance and wrongness. But that's the situation you're in if you're knowledgeable. Railing against it only makes things worse. Being able to contain the annoyance, so that it doesn't drive your communication, is a hard prereq for doing something good about it.
King Canute was supposed to stop the tide, you couch alluder.
No, he was demonstrating to his fawning courtiers that he couldn't stop the tide. (Apologies in advance to the parent commenter @pvg if my irony / sarcasm detector is out of calibration.)
https://en.wikipedia.org/wiki/King_Canute_and_the_tide