"I guess My logic is strange in that I don't know what my tortoises need for good health and development."
Well, you do know to some degree by reading field research. You know they don't eat hot dogs (I'm being silly). Wait, we do know that some of them will eat hot dogs (or newspaper, or candy, etc.) , so going by what they *will* eat versus what they *should* eat isn't an approach that I would fully endorse.
I agree with your varied diet approach. Right now there are a limited number of weeds and clover in my yard, so I have to supplement with endive and greens from the Brassica group. I know Brassica's have potential problems, so I throw in what weeds I can find, and make sure the torts are warm and hydrated and supplemented.
Now if I throw in a couple pieces of Sassafras do I think their little livers will explode? No. Can I think of a good reason to recommend using it at all? No. If a reptile's physiology is different enough that it can eat some foods that are poisonous to us, it could also be different enough that a mildly toxic food (to mammals) could be moderately toxic to them.
Since I don't know the answer, I won't use the food. It crosses my line of caution. Brassica's, when "part of a varied diet", have worked well for lots of tort keepers. Maybe in a few years we'll be saying sassafrass is a good part of a varied diet. But without anything to back it up, other than the torts seem to like it, I won't be using it.
PS - just so no one misunderstands, this all boils down to where I draw the line. I definitely don't think any less of anyone who uses sassafras. Or even hot dogs. Well, maybe hot dogs.