What you say is true, but disingenuous. It is like saying that British common law is just adherence to the principle that judgments should be made in accordance with principles that were accepted in previous judgments, and it varies widely across different jurisdictions. This is true, but British common law means a lot more than just that.

The same is true of Sharia law. It has a lot of baggage. And it doesn't always read as a Westerner might naively like to read it. In particular when it comes to Sharia law, opposition tends to center on items 2 and 4 on your list.

On #2, Sharia law protects the family, but with different definitions and severity than Western society accepts. Consider the asymmetry between men and women for divorce. Consider the punishments for adultery. Both are widespread in Sharia law, and neither is palatable to Western audiences.

More problematic is item 4. It is not (as it is in the US constitution) the protection of freedom of religion. Instead it is the protection of the Islamic religion. (With limited protections for peoples of the book.) Thus we get anti-blasphemy rules, punishment for converting Muslims to another faith, etc. This is in direct conflict with core precepts of the US Constitution. This is not an accident of interpretation. It is a central feature of having a system of law whose purpose is to support a specific religion.