It seems like there are stories for all parts of the spectrum on whether or not the black locust is poisonous to livestock, people, gardens.... And people say its amazing for so many purposes and plant it around livestock, use as fodder, eat it themselves, others say it kills everything.... consensus? Thoughts?
If you will indulge me a story for a moment, I think it might help.
Vidalia onions have a higher sugar and water content than other onions. When they were first developed by Moses Coleman in Georgia, he was shocked by how sweet they tasted. At first, they were so strange that no one was interested, but eventually he found a market. They grew to be hugely popular, but an interesting thing happened. While the breed was fully stable, it didn't develop as sweetly in other parts of the country as it did where it originated. The originals were able to be eaten out of hand easily, but those grown elsewhere had a slight bite to them. As it turns out, by fluke of where they first appeared, the local soil was very low in the sulfur content that normal onions used to generate their hot bite. Between the low sulfur and unique nature of these onions, they were extra sweet. But it only stays that way in similar soils. In normal soil, they are not quite the same flavor and extreme mildness. So what is the point of this story in relation to the question?
Simply this: Nothing says that both sides of the argument can't be right. I have no doubt there are some parts of the country where the toxic elements of the plant get concentrated. Maybe certain naturally occurring cultivars are stronger than others. Add to this how weather can affect them (Dry climates vs wet) or what each person is doing to them (drying the leaves before fodder vs fresh), there is a lot of variation there. As I understand it, in too large of doses it is poisonous regardless of the plant in question, but in lower doses it can be safe depending on the factors mentioned above. Small doses are considered medicinal for animals that self-medicate and there are some animals that seem to have a much stronger tolerance to whatever may or may not be toxic in the plant. Even the genetics of the animal or person in question can be a factor.
I would say ask around your location first for what is the common wisdom and use that as a baseline. If locals are all saying it is safe, it probably is locally. If they all say it is poisonous, your local conditions and variety may indeed have much higher concentrations. Once you establish a baseline, you can then go from there and determine how true or untrue the statement is. I think in small doses, any variety is probably safe as long as the person or animal in question isn't particularly sensitive. Even if people were saying something was absolutely safe, I would still act cautiously at first just to be sure.