Isn't the capitalistic way that any company can choose their customers? By the way Amazon is not preventing anyone from hosting Parler. They are just not doing it. That's like saying you can what ever you want; I do not have to let you do it from my front lawn.
If a baker can't choose who to make a cake for, why can a tech company choose who they can provide services too? My biggest problem with this Amazon example is that in a PaaS/IaaS type situation they are just providing infrastructure. It's not obvious to most users what infrastructure a website/app is running on and there is little to no harm to the Amazon brand.
"If you don't want your dog to have bad breath, do what I do: Pour a little Lavoris in the toilet." -- Comedian Jay Leno