While some people get a bit cargo cult about things there is a rough consensus that XML is good for some things and terrible for others whilst JSON is the exact reverse ;-)
I personally rather like YAML for anything intended for humans to read and edit.
If XML didn't have those idiotic verbose closing tags, this probably wouldn't even be a discussion. Or if JSON had comments and didn't require quoting all keys.
What's funnier is seeing the HTTP/JSON folks re-invent SOAP. But maybe this time it'll actually be Simple.
XML is fantastic, all data XML!
XML is horrendous. All data in JSON. I can't believed we were using this awful XML!
JSON is sooo lame. XML is the new JSON!
Same for languages, frameworks, programming patterns, etc...
Even more volatile than fashions.