By default, Lemmy allows downvotes globally. However, when a server disables downvoting, it is similar to using a feature that is usually reserved for enterprises and very small, non-federated communities.
If a user prefer to not see downvotes, they can disable it by his favourite client settings, but the rest of the community should not miss this functionality for the pleasure of few users.
If you simply forced the ordering to be by new/newest comment, votes in either direction would become irrelevant. But that also means that only the most active users will ever see a bulk of the content when it is relevant, or at all.