Is it appropriate to discuss the tags on a story in comments?

No, it is not. Such discussion should take place in PMs or perhaps in a forum topic like this one.

Think about it. The comments are supposed to stay with a story. Discussing the tags puts the author in the position of either agreeing with the commenter and changing the tags, in which case the comment is rendered meaningless or disagreeing with the commenter in which case the comment thread becomes tangential to the story as the author defends their position. Either way, it can't help to detract from the value of the story as a story.

So, suggestions of tags in comments on stories are inappropriate. Authors can ask me to remove such comments, of course, but I may also remove them myself if I notice them. And I won't necessarily send a notice to the commenter that I have done so; life is too short to get involved in defending a common sense policy.

Note that tags are for authors to communicate to their readers; the only REQUIRED tags here are those for explicit sex content, for fanfiction, and for verse. There are RESTRICTED tags, like the contest tags are only for contest entries and the General Audiences tag cannot be placed on anything with explicit sex scenes or discussions and the Selected Themes cannot be put on anything that has a mature theme. Some universe tags are also restricted. The Solo flag is also restricted for stories that are complete in one posting.

Everything else is up to the author. You don't like the story and feel the tags are wrong, either communicate with the author in PM or start a (friendly) forum thread or blog.

Hugs,
Erin