Strong disagree. We ended up with a Markdown-like menagerie of parsers and serializers with varying degrees of spec-compliance and non-compliant options. In practice, there are plenty of config files that consist of json-with-comments.

I'm good with banning comments in mostly machine-targeted files. But human edited config files that I work on are mostly json these days, and have been. The "_comment" field is not in any schema. No receiving system will read it, other than to throw for schema-non-compliance. I want to leave a message for other human readers inline. If comments would have killed JSON, then we shouldn't have adopted it for config files, because I guess JSON is killing config files?