For people not used to the HN / Reddit point system this requires some learning. I had my fair share of "I second this" posts and took my down votes.
As long as HN is growing and new people, who are used to pin boards and mailing lists without a voting system, come in, you will have this problem. Just down vote them if you have ability.
Maybe, this should be more emphasized in the FAQ [1]. When I signed up here recently it was not obvious to me, that such posts should be avoided.
This community should try to stop a decline in quality...