EDIT: You should realize something, that spammers might create 10 accounts. 1 account that makes a comment, and the other 9 accounts would vote up for the other account's comments, to increase the karma and pass the karma threshold.
But it won't be an effecient solution, according to briansmith's approach.
Spammers could hire users to comment.
Here is how I imagine it:
1- Spammers crawl the submitted article.
2- Ask real users to read it and comment on it.
3- Copy what users said and submit it automatically here.
4- You will think it's NOT a spam, and you will up-vote what the spammer commented, and this will allow the spammer to submit content and the problem won't be really solved/ but reduced.
Your suggestions seem reasonable... if it gets to the point of an all-out War On Spam-bots. Unless things get that bad, it may be sufficient simply to make it a little more difficult for the spammers (so that they go hit on other sites). Meanwhile, I doubt that many spammers are going to go to trouble to create the mutually-supportive accounts (and certainly not actually spending money by hiring live users).
About hiring live users... it will be a slave hiring, without paying money.
Here is how it works, just one of these 2 options:
1- Spammers automatically create a blog, crawl the submitted articles here to their blog, and wait for a real user to comment on it, and then submit that comment here.
Or: 2- Spammers would create a bot that crawls the submitted article, submit that article to any public social news website, and wait for real users' comments, and then automatically submit the real users' comments here, and you will think it is NOT a bot/spam, but it is.
EDIT: This is something that can be implemented these days, not after a decade!
If this happens, will you think that this is a bot or not?
If one adopts the concept of many different karma thresholds, then it becomes trivial to say that only users with X karma can upvote. Set it to some modest level, and when they hit X karma, new legitimate users will feel rewarded for their contributions!
I agree that there will always be gaming strategies. I just think that having gradually increasing rights/priveleges at quick incremental karma steps is a good way to combat spammers.
This is similar to what I wrote here: http://news.ycombinator.com/item?id=506028 Users should have a history record.
But it won't be an effecient solution, according to briansmith's approach.
Spammers could hire users to comment. Here is how I imagine it: 1- Spammers crawl the submitted article.
2- Ask real users to read it and comment on it.
3- Copy what users said and submit it automatically here.
4- You will think it's NOT a spam, and you will up-vote what the spammer commented, and this will allow the spammer to submit content and the problem won't be really solved/ but reduced.