Must opinions be substantiated? (TMT examples)

[randomq]

Though we in general don't require people to substantiate their religious beliefs, we DO require substantiation when they attempt to gain privileges or rights over others from those beliefs. Typically, historical precedent predating whatever change society wants to make. Otherwise we'd have people using the religion card for anything that annoyed them, just to get their way.

I don't think it's trolling to ask someone to back up a particularly unbelievable claim. Perhaps not to a legal or scientific standard, but at least throw out a link to an article on the web or something. Otherwise I can make any claim I want in my arguments.