It depends on the dog, IMO, if a resource guarder should be put down or adopted out. I think in most cases the dog needs to go to a rescue or foster home with a trainer, before they're adopted out to someone.
I think if a dog gives a warning growl when their food is approached, lifts their lip, and even goes to snap or bite at the hand going into the bowl, can usually safely be adopted to an adult home with some dog experience.
If a dog is A SERIOUS guarder, with a bite history, bites without warning, or really attacks the hand or goes for the person rather than just giving a bite and letting go when the threat retreats...if they can't find a trainer home, they should be put down. It's sad...but it's a big risk.