Steve Sailer points out that U.S. judges have used foreign law (e.g. English common law) in decisions since the U.S. began.
However, I think the issue here is that we do not want to overturn previous American precedents based on what European countries are doing; particularly in areas where the American political philosophy apperas to be diverging from the European one (plus, as I understand it, judges are looking at precedents from countries other than just the Anglosphere).
I may comment more later; my thoughts are not entirely formed on this.
That is all.