I remember when the worst thing one said to a Libertarian was that they believed in open borders. Now it is mainstream Republican/socialist thought.
I don't think "open" borders is the right way to describe those who believe in free trade.
Open borders implies there is no control about what or who comes across a border.
Free trade is compatible with security checks for both goods and people coming across, and can designate certain goods and certain people as illegal for entry.
Open borders does not describe my position at all.