It's worth remembering that this principle was upheld by the Supreme Court a little over two years ago, in the case of a baker who refused to bake a cake for a same-sex wedding: https://www.nytimes.com/2018/06/04/us/politics/supreme-court...

In this case, it was decided that the baker has a right to refuse service if they have a moral objection to the service they're being asked to provide. The same principle applies to Amazon, though one can certainly see how the scale and scope of Amazon's services and their centrality to the online economy makes things a bit more complicated.