The book is selling well largely because efforts taken to attack it have simultaneously given it free publicity. The post above has done exactly that. Seeing this phenomenon play out over and over again in my Twitter feed is crazy.
But what is crazier is that I have yet to see a compelling explanation for how the book is actually transphobic, false, or biased (and this doesn’t surprise me at all). The absence of a fact-based refutation only makes its more likely people will buy the book so they can see what the hubbub is about. More book sales, more people reading it, more people influenced…exactly the opposite of what the book’s critics would want, I’d think.
In response to the OP, the lesson here is that corporate attempts to block undesired speech can easily backfire when consumer demand for that speech (or any speech) is high. I suspect this why it’s not seen as a hugely worrisome thing. That said, we shouldn’t bank on always having a consumer population that values freedom of thought and access to diverse opinions; if we lose that, then our purchasing power will cease to be an effective check against corporations.
ACLU relies on donations and so it is not immune from this economic pressure.