Why is this such a pain point whenever an internet discussion of freedom comes up? Free speech and freedom are principles. These principles inspired the guarantees the Constitution claimed to make. But that does not mean that the government is the sole arbiter of freedom. The fact that Amazon bans a book means that Amazon does not appreciate the value of freedom and free speech, in the same sense that when the government limits speech, it means they do not value free speech and freedom.

Freedom isn't just with respect to government. When Amazon filters books you can buy, that does mean we have less freedom, especially when Amazon is a filter through which we are able to purchase most goods. No, your first amendment rights haven't been violated. But yes, we have less freedom.