To flatly reject the author’s argument just proves his point. Specifically that folks don’t consider the origin of American values and law (he used the Constitution as an example if you recall) as being Christian. This is also why he didn’t mention the other belief systems you stated because they weren’t considered when America was created.

Secondly, just because someone claims to be a Christian doesn’t mean they are. A true believer in any faith would hold fast and true to all of that belief system’s values. He made note of this by pointing out “Cafeteria Christians”. It’s the same as blaming the law when it’s really the application of the law that’s the problem. Socrates and his willingness to drink the hemlock is an example of this.