If you want to understand a literary work, you need to understand its context*. That context includes the author, but also when it was created, the original medium, the culture it's from… and the readers. Yup, people shape the work as they read it, and sometimes in ways that cancel out what the author said. But the voice of the author is still there. You can't simply ignore it; at most fight against it, and sometimes win.

Now, let's say the author is bad, but the work is good. Then it stops being just a literary matter, to become a moral one. It's all about weighting the harm caused by the author (and, as you said, subsidising that author and their problematic views) versus the benefit that the work itself would give to potential new readers. There isn't a single right answer that'll apply to all works, I think.

For example. Lovecraft was a racist piece of shit. But he kicked the bucket already, and his books are in public domain in most countries. So no matter how much you talk about his books, and how many readers pick them up, you aren't really financing a racist. So I guess it's fine? One might argue the racism leaks into the work, but remember what I said about readers being able to fight against the voice of the author?

Then there are cases like Harry Potter. We know JK Rowling is a bloody TERF. And if you buy her books, it's money being given to someone who will use it to promote her shitty views. One might say "just pirate them!", but plenty people won't pirate, and they'll know about the work because you talked about it. Then IMO it's getting into yucky territory, the odds you're causing harm by promoting that work are getting bigger, for a relatively small benefit people would get from the work itself.

Just my two cents.

*by "context", here, I mean everything around the text that shapes its meaning.