"You are probably right in the specific case you outlined in your post, but blanket statements that no two reptile species should ever be kept together is not accurate. All zoos do it."
My statement was in regards to casual reptile hobbyists doing it, not zoos. If you want to bring zoos into the discussion we should mention that most zoos have tons more experience and qualifications than a person keeping reptiles as a hobby, so it's more acceptable. They have the time, expertise, funding, and all the proper requirements to do it succesfully. That doesn't mean we should try it at home. Most causal reptile owners do not have the know how and understanding of these animals to do it properly.
Not to mention, when animals are placed in the same enclosures at the zoo, it's because they are all from the same habitats. Alligators and turtles come from the same habitats as do chuckwallas and desert iguanas, so for these animals it is perfectly natural to be around each other. Uromastyx and bearded dragons, on the other hand, come from completely different sections of the world. They would never cross each other's paths in the wild, and putting them together in captivity is not a natural thing for them. Just because they are both from desert species doesn't automatically mean they share a habitat. Add to that the fact that males of both species tend to be quite territorial and agressive to other males, so if you get one of each in the same small cage you could have a serious problem on your hands.
"Rail on the Dallas zoo if you want, but I think they do a far better job than most keepers, so attacking them isn't constructive."
Maybe they do a better job than most casual reptile owners, if only because too many reptile owners are uneducated about proper husbandry. Compared to other zoos, though, they do not do a better job than most. Using them as an example of how this husbandry is ok is no more constructive than attacking them.
Besides, I've never seen them housing beardies and uros together anyways. Do all those other zoos house beardies and uros together specifically, or are you referring to the iguanas and chuckwallas when you say they house multiple reptiles species together? I've been to a lot of great zoos in this country, but I've never seen beardies and uros in the same enclosure that I can recall.
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2.0 bearded dragons (Ocho / Domo-kun)
0.1 kingsnake (Rio)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)