It infuriates me when I see regular people being turned away from adopting a dog. Sure, some homes aren't suitable for all dogs. I wouldn't want a huge and/or high energy dog in an apartment, and I wouldn't want any dog in a home where they're tied up outside day in and out. For the most part, people should be allowed to adopt! I've worked in a shelter environment for several years and it sickens me to see other humane societies turning adopters away. Typically these places are also euthanizing a lot of adoptable dogs.
The shelter I'm working at right now is perfectly located next to 2 other, larger shelters that turn away a lot of great adopters. It benefits us because there is a flow of rejected people coming to our shelter to adopt a dog. They usually walk in and ask "can I adopt a dog here?" To that we ask if they had been to a neighboring shelter.
I don't think that people must have a fenced yard or that it be required to have previous experience with a particular breed before being able to adopt, though it makes it easier. There is no such thing as the perfect home. Dogs don't deserve to rot in kennels until the unattainably 'perfect home' comes along, because it's not going to happen.
Let the dogs get adopted!