Personally I'm pretty against taking anything besides a dog, cat or maybe a larger "small furry" pet like a rabbit or ferret outside for a walk. There are so many variables outside of the owners control which could come into play. Small animals are really vulnerable to attack from dogs being walked or wildlife, and if they escape it's much harder for them to survive as natural "prey" creatures than it would be for a dog. I think they're also harder to catch; many domesticated dogs will approach a non-owner if they'd escaped but I don't see a rabbit or snake looking for humans who might be willing to take them to a vet or shelter!
There's also the issue of vaccinations... I currently keep hamsters and I really don't know enough about what diseases they might be able to pick up outdoors. I used to walk my rabbit in my own garden but she had the "full suite" of vaccinations to go outdoors. My hams don't have any as the vet didn't recommend any, but I believe there are diseases of mice/rats that could affect them, so I don't intend to take them for a walk anytime soon.
And one final problem with the snake walking dude (I don't usually write such angry-sounding posts, haha, I just got a little carried away here - I'm always a worrier about pets' safety) is that there are quite a lot of people with serious snake phobias who might react badly to his pet... I know there are people with dog phobias and we don't all stop walking out dogs, but 1) I think snake phobia is more common and 2) dog walks are essential for welfare but snake walks aren't!
