It does depend on who created the base. If the base is an original piece and the creator set a free to use rule on it, then it is OK. Especially if you asked permission or your art is more using the base as a reference, not tracing it.
If someone is selling art or commissions, then they shouldn’t be using traced bases of other people’s work. They could get into legal trouble with the original owner of the art.
I do also feel like people on the internet try to play vigilantes and end up harassing or dog piling the artist. I think just reporting them is more effective then becoming sort of obsessed with hating on them. My guess is they are probably some small artist who most people never heard of and it’s sort of not worth getting too angry at them.