"it makes great sense to have a temporary ban on countries that export terrorists.
He could say he opposes serial killers working in child care and the left would protest and big tech would file lawsuits."
OK, let's try to compare those two statements rationally. Let's look at the second. Being a serial killer would be something you know about the person. Can you give any credible argument why "the left" and "big tech" would object to such a person working in child care? Really? Of course you can't.
Now let's go back and look at the first statement. Most countries that "export"* terrorists (to use your hyperbolic description) are actually populated by people who are not terrorists. So you really don't know anything much about any particular person coming from there.** This is a very different case to limiting the activities of someone of whom you know a great deal on the basis of knowledge.
It's sad that we have to give basic lessons on thinking to el Reg readers.
* Let's not forget that the US "exported" terrorism to N Ireland by failing to stop individuals and organisations financing it.
** Except, for instance, that they're just a tourist trying to transit through a US airport on their way home from holiday.