Opponents say [Idaho's law] is an unconstitutional prohibition on interstate travel and free speech rights.
That's because it IS an unconstitutional prohibition on interstate travel and free speech rights!
It's as unconstitutional as hell, as are any other red state attempts to restrict where their residents can travel and what they can do when they get there. I suspect a lot of red state legislatures realize that, which is probably why more of them haven't bothered passing a law like the one in Idaho.
To the lawmakers in the Idaho statehouse: Dudes, for you have any idea how ridiculous this law is making you look? (Rhetorical question, they obviously don't,) There's this document called the US Constitution that you need to read. Among other things, it says you get to make laws about what people can do
in your state. What you don't get to do is restrict where your residents can go if they want to do a thing you've outlawed that is 100% legal elsewhere.
Idiots.