Precisely. Maybe we shouldn't be focusing on Amazon's alleged "censorship", but rather on what makes us react to it in a rather similar way as if the government did the same thing.

The choice of not doing business with someone ceases to be a meaningful choice when it's the only viable alternative. One could argue that Amazon is not the only viable alternative and that argument is, strictly speaking, correct. However, this isn't a binary situation -- one day we have plenty of equally viable alternatives and the next day it's just Amazon -- but rather a continuum.

TL;DR: Amazon pulling stuff from their store is only a bad thing when taken together with not having a meaningful alternative. The latter is a bigger problem than the former.