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.
Sellers being also part of the problem is a fair point. But it isn’t just about Lemmy being Lemmy; it’s that unless a community disallows sellers, amateurs eventually leave.
This would probably need a different approach, like different comms for sellers vs. amateurs. Or, if the tag system were to be implemented, forcing people to tag their content accordingly.
About sexuality: the reason why I think that tags would’ve worked is that, once legitimate-but-shortsighted users stop downvoting things based on their sexuality, the trolls stick out like a sore thumb. And then you can simply kick the trolls out.