Where's a camp checkpoint? Do you start out on a map always knowing where one is? Which way is it? What do you do if there's no camp checkpoint around and you're tapped? Reload and lose possibly several hours of progress?
"Okay, the camp can remain in one spot, but you have to walk back and forth to it." If there isn't any threat around, what does the walking do except add padding?
I agree that there has to be some form of resource management revolving around long rests. A cost-free long rest makes the Warlock class too weak compared to Wizards or Sorcerers, and thus pretty pointless to play. There are things which could be done to tweak the long rest system, but I don't think forcing rests at specific locations (especially in cities) is the best solution.
