Not a religion, but a term with a specific meaning, which meaning implies a collection of freedoms granted without discrimination. People are welcome to use licenses that revoke those freedoms, but calling them FOSS is confusing and muddies the waters.

See Llama's license: if it can be Open Source while having restrictions, then having an Acceptable Use Policy is okay, right? So Redis could create a license that bans its use if you host adult content, Star Wars fan fiction, or documents containing the letter R?

If Open Source doesn't mean a license that indiscriminately grants a set of specific freedoms then it's pretty useless as a term—all I know on hearing it is that a project's source code is available. Which reminds me, we already have a term for that: Source Available.