Wait, hitchhiking is illegal (in the US presumably)? (Supplemental question: how do you make hitching illegal?)
In the UK I've met many interesting people both while hitchhiking myself, and while picking up hitchers. It is a practice that seems to have almost entirely disappeared here, not because it's illegal, but I guess because most people now have cars and some "stranger danger" worries.
As for "how": legislature passes a law against it like any other traffic law. Similar to jaywalking or prostitution (soliciting sex on the side of the road).
In the UK I've met many interesting people both while hitchhiking myself, and while picking up hitchers. It is a practice that seems to have almost entirely disappeared here, not because it's illegal, but I guess because most people now have cars and some "stranger danger" worries.