One of my favorite post-election action newsletters (which you should subscribe to if you're looking for actionable ways to resist the Trump agenda) covered the Milo Yiannopoulos/Simon & Schuster problem the other day. I suggest you read it if you're looking to take action: It give the address of where to send actual letters, which the activist suggests doing because actual letters make an impact in a way that emails can't. I'd also suggest that you direct these letters to the Threshold imprint.
The activist I'm linking to here does not support a boycott, and I'm inclined to agree, though halfheartedly. We are both Simon & Schuster authors, so please take that into account. I genuinely believe I'm ambivalent about a boycott for reasons having nothing to do with my own affiliation with S&S. (For the record: Unless "Face Value" unexpectedly and literally becomes a bestseller, I won't get any more money out of the company than what is promised to me in my contract. Most authors never earn back their advance and unless something drastically changes for me, I'm among that crowd.) I think boycotts can be effective. But they need to be strategic and organized for them to be so, and I just don't think that Simon & Schuster is the best target in this way. Not only because it's a fragile industry (though honestly, that too) or because they publish wonderful, often progressive, authors under different imprints (which they do, but that in and of itself is no reason to not boycott them) but because nobody gets into publishing to make money. They get into publishing because they love to read. They love books and ideas. This is one of those cases where writing a heartfelt letter actually might make a different for future buying decisions, particularly if there's a critical mass where the assistants opening the mail can make a case to their higher-ups for not publishing more white supremacists because it will simply be too much work.
So I suggest you write letters—physical letters, even if you've already sent an email—and then completely ignore it, though depending on how the book is received that tactic might need to change. No books are sold without publicity surrounding them, so let's do our best to not give this book publicity. It's tough because I very much feel a responsibility to speak out here, but I also know that I'm probably a part of the problem by doing exactly that. I've never been targeted by trolls on Twitter as much as I have been for my tweets on this topic. White supremacists love our outrage. That's not a reason to not be outraged! But it's a reminder to be strategic about it.
All that said, I'm not going to tell you to NOT boycott Simon & Schuster; if you choose to, please don't feel like you need to apologize to me for not buying my book. I'm still figuring out my own ways of how best to resist, and I support most endeavors to do just that, even if it's not a tactic I myself am engaging in.