Edit: yeah, karma is needed.

Actually I think it would be incredible useful.

You could use it to shift a community to a more useful direction.

A more direct way of eliminating common errors.

If on a cool new tech that's renewable if someone starts another bloody global warming discussion being able to downvote as OT could try and keep people on topic rather than having to down vote something you agree with.

There are issues with the idea, it can become censorshop, but I find it an interesting one.

You could blend colors too. Reddish-purple = off-topic troll. Dark orange = weird and scary troll. etc.

Edit: another thing I should have mentioned is that it seemed to me that only those comments made after I gained this ability were downvotable, the thread my last few comments were in was sprinkled with downvotable comments, which were newer, and non-downvotable comments which were there before mine. I might have been imagining this or be mistaken though.

EDIT: checking again at 507 and I now have the power to downvote. So there's our answer (plus my moderately shameless play for some upvotes worked).

https://xkcd.com/1224/

I think you might be mistaken. You might not have noticed yet that the downvote option disappears on its own a set time (24 hours, I think) after the comment was made. Perhaps it was only the comments older than this threshold that were non-votable?

I think my karma accrued overnight, so when I noticed I'd exceeded the threshold a lot of the thread was perhaps a day old. The only thing I am relatively certain of is that some of the older comments in the thread were not downvotable, and the newer ones were.

That would be quite computationally intensive to implement.

How about a tag system associated with each posting? Then you can have just a scalar "weight" and a set of keywords (string labels), each with a designated meaning. You press a "plus" button or something, and a menu with optional tagging pops up (tag clouds can be used).

Some tags could be "spam", others could be "didn't read" and users can build their own threshold filters for tags. (0) spam; (4) didn't read; (3) incomplete; ...

As for "didn't read", if you're not interested, just move on. If you think the article is inappropriate and can, flag and move on. If you see a comment that looks like the poster didn't read the article, you can call civilly call out what is in the article, and perhaps down vote the comment.

Yeah I thought about this very hard actually, and came to the conclusion that just a "weight"(+) button is enough.

And, if you care that much so that you would waste your time providing more ... contextual meta-info (about the weight itself), you simply need a pop-up and a quick way to select words from a common dictionary. Certain users can even make content "more spammish" by simply increasing the weight with a click (they agree with the labeling and they are "special" in some way).

This, and the weight itself should provide enough info for a comprehensive "decoration" of the postings.

I can't fault you - slashdot hasn't been relevant for.. at least a decade.