It won't fly in the US, other countries might comply. If actually implemented, an unintended side effect might be a defacto ban of UK academics and researchers in the US. Legality aside, most corporations and academic institutions here being told by a British researcher, I'll come, but you can't have any Israelis/Jews on the project will be told to stay home.
In terms of the U.S. what you stated is very true. We should recall there are various forms of reciprocity :)