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.
Lemmy is the ultimate embodiment of a free market. U dont think thats even a valid argument if that content is downvoted communities dedicated to it will be equally downvoted. Welcoming should not mean making the experience for the majority significantly worse simply to avoid a minority having to search a little harder.
Blocking communities doesnt work entirely since u end up with fat chicks and dicks in communities that arent specificly dedicated to either.