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.
Certain tools inspire certain behaviors. In other words, all you have is a hammer… Ironically, that’s also a reason commercial platforms resist implementing negative votes.
Changing the tool to better suite it’s purpose is an option, but decentralized networks are inherently resistant to such changes. With the backlog of bugs and missing features this ecosystem has, the developers would not be amused if somebody came up with a new tagging or filtering system.