The difference is that the dose people are taking is very light (the dose is for a 10lb dog). I doubt most people know that the average dose of fenbendazole for a 100lb dog would be toxic to people.
I tried some, and my fleas are gone.
On the other hand, stage 4 cancer patients are taking 1200 mg daily, with good results. There are many Facebook groups dedicated to Fenben and other alternatives for cancer control. We have become our own oncologists, using standard of care medicine for support as in advice, imaging and acute care.