Well, one could argue if just posting a link with a title is a ‘quality’ post. But the topic is still worth a discussion so I don’t see why it should be downvoted.

I think you should not downvote a post you have a negative opinion about. If the post is worth to discuss then why should I not upvote the post and then say that I disagree in the comments. If we all down vote those posts nobody will see it (apart of those who sort by controversial) and there will be no discussion.