I don't like downvoting because downvotes are so ambiguous in meaning. An upvote clearly means "read this!". A downvote could mean disagreement on the subject, dislike of the author or just disinterest. I might want to read a story with wich many people disagree, but I might not want to read one that everybody finds completely irrelevant or shallow.

The trouble is that the meanings of up and downvotes are different for news stories and comments respectively. For a comment, the votes almost exclusively mean agreement/disagreement. Only in rare cases do I disagree with a comment but still find it so important that I vote it up. This is different from, say, a scientific paper where this happens frequently.

Overall I think downvotes are unnecessary and cause a lot of bad blood.