The XSF has a fantastic page dedicated to debunking common XMPP myths. Here are a few examples:
• XMPP is XML, so it must be slow
• XMPP isn’t secure
• XMPP doesn’t protect privacy
• XMPP is too verbose
• XMPP is unreliable
• XMPP isn’t suited for the web
Of course, all of these are misconceptions.
You can read the full explanations and clarifications here: https://xmpp.org/about/myths/
Are there any other XMPP myths you’ve encountered that you’d like to see debunked?