Communities won't really stop downvoting, and shouldn't— but, with that being said, downvotes are a way to shape a feed right now. We don't have a good way to find the things we want, and when we do, there is the perception of what fits together as good content and what should be seen.
Communities will provide a few thing that will help with this- the ability to create places to gather content according to rules decided by groups of people based on... whatever they want! Easier to find, and easier to curate the experience. This means that the feeds can be shaped and cleaned up without ever using downvotes (depending on what the goal is) and without worrying about impacting a post outside of the community view. It allows for a lot of flexibility and really encourages a place where people can gather. The features it will bring also are also encouraging when it comes to being more engaged.
We can't completely change human behaviour, but a lot of it has come up because we were missing the flexibility these tools will give us, so the balance should swing back towards a more reasonable middle ground. I'm glad they sound like something that will interest you!