I think looking at this issue with the example of "Parler" may be missing the point. The issue worth debating is surely not whether Amazon made the right decision. Of course they did. The issue worth discussing is who gets to make this decision in light of what the decision implies. Due to how much businesses are choosing[1] to rely on companies like Google and Amazon as service providers, these "tech" companies can easily kill other businesses by denying service, without violating any laws in the process.
These "tech" company middlemen are generally not treated like utilities under existing laws but the question is whether they are being treated as such by customers, the public.
1. Perhaps not so much consciously choosing as being persuaded by tech company salespeople and, IMHO, biased "media coverage" (=hype).