If your goal is to create a service that's main feature is content discoverability, I would think that tags are essential. It would provide you with great metrics for knowing what the user prefers. For instance, "They tend to tag lots of funny stories on Saturday. The tag tech news on Monday and Tuesday. They tag movie news on Thursday." Your recommendation engine would then be able to suggest articles to them. "Other users have tagged these stories as tech news and it is Monday. Here's your Monday feed!" I'm not saying you can't make a working product without them. I'm simply saying you probably can't make a competitive product without them.