I think nobody is screaming here that this particular action is illegal, as I read the comments. However, there is many things governments can do, that can be considered (under different subjective considerations) unethical, following a hidden agenda or plainly stupid. My personal decision at the moment is that I do not travel to the US. Which means that at times our papers are not presented at US conferences because my PhD students don't get visa (even unrelated to the current ban). I think the US will survive this particular loss though.