May I ask why you believe this? I checked Amazon, and found a few books written by people with CF. They aren't best sellers, but all of the ones I've looked at have sold at least some copies, based on the reviews. Your own story would be different, and uniquely interesting.

I realize, as I'm sure you do, that one can't pursue every possible avenue when trying to generate an income; there's only so much time in the day. So maybe writing an ebook about your experience is not the most promising thing to do, in your mind. Then it's a judgment call to decide where to put your efforts.

People are routinely dismissive, attacking and ugly

For this reason, if it were me, I'd keep that content separate and anonymous (I would have done this from the beginning, because I know how these things go). But that doesn't mean you shouldn't write it.

FWIW, earning an income is not necessarily in line with self-promotion. The vast majority of people who support themselves do so in relative obscurity.