Great question OP. Does this ("my seminal influence turns out to be a douchecanoe") apply to comps too? I read a tweet by an agent claiming they will not look at anything comped to Ender's Game, since (according to the article listed in the tweet, anyway) Orson Scott Card is an avowed homophobe.
Are we torturing ourselves? Sure. But we're also trying to be sensitive.
And, by the way, does this apply to pitches made to editors? Aren't they looking for comps and influences? I was under the impression that that was an important piece of the pitch.
Any information anyone can provide on this will be very helpful to me - all this stuff is swimming in my head and I'm trying to quickly make sense of it.
The purpose of comparing your book to another is to give the editor or agent (or reader) a sense of where your book belongs on the shelf.
You can be influenced by books that are completely unlike your book in tone, style, plot and category. An example of this is that I often say one of the best books I read about writing is in fact a book about music.
That book is an influence but unless you're writing essays about music, it's NOT a comp.
If you are writing a crime novel about a man who encounters people doing bad things to folks for money, well, you might use Lee Child as a comp even if you've never read a Jack Reacher novel, let alone been influenced by one.
Influences are more about how you got to be the writer you are today.
Comps are where a book store is going to shelve the book you wrote.
As to agents saying "don't comp to Orson Scott Card" they're telling you something about their political beliefs.
A savvy writer would NEVER use Ender's Game as a comp. It's old, and it's an outlier. It's the same reason you don't comp to Stephen King, JK Rowling, and Dan Brown. Your comp books should be recent (within two years) and by writers who haven't published one gazillion books. In other words, fight in your weight class, don't assume you're a heavyweight quite yet.
As to your question: comps are relevant, influences are not. And both are secondary to the story of the book you're writing. That's all I care about. And it's all readers care about.