I pretty much knew what I would find in the comments on this one. The right to roam, in country in which it exist in one form or another, is exactly this: the right to roam. Not the right to camp (although some allow it usually with some restriction), live, squat, pollute, destroy, ...

As someone who sometime had to go from point A to point B in the countryside without a car, this was a necessity as it was the only safe way to do so (sidewalk are nonexistent in the countryside). It also avoid "trapping" some public land within private one (and effectively privatizing it), although, in my country at least, the state will usually preempt a small piece of the private land to always have a passage between public land.

As for the liability, is should go without saying that there is usually laws that release you from any liability for people hurting themselves while roaming on your property (with the obvious exception that you should not put anything with the intention of hurting people, for example traps).