For anyone interested, either just out of curiosity or because they'd like to read or write fanfic without feeling like a horrible criminal and scum of the earth,
this is a good list of authors' stance on fanfic (not exhaustive and covers mostly authors, not rights holders of films/TV shows, but it's a decent start and all quotes there are supported by references), with both pro-fanfic and anti-fanfic authors listed.
Of course with any individual creator, it's always an idea to do a Google search in addition anyway, especially if the quoted reference is many years old, as creators' attitudes and opinions can and do change over time; mostly it seems it's formerly anti-fanfic authors who have either become neutral or explicitly pro-fanfic over the years, but I'm sure it can also happen the other way around.