It is morally wrong to buy up tons of land, then forbid others to walk across it. Land should be for everyone, not just for a select few, especially since land was not created by the owner.
All land owners could forbid others from walking across, that is indifferent if you have 1 land-owner or a million. That's the origin of rent: becoming a land-owner makes you one of the forbidders.
In the UK, there are public byways and footpaths, which allow a specific right of way through private land. Often times it is a path through a farmer's field or such. The US could establish similar rules.