If taco bell is sending you to the bathroom it’s because you’re ordering beans and you’re not used to beans and lots of fiber. That’s not the fault of taco Bell.
Also, it’s the easiest fast food option for vegetarians and vegans, and as such has (in theory at least) a much better environmental footprint than the others. Fast food ain’t great, but Taco bell does not deserve the reputation it has. And while I am absolutely not assuming it’s why you said it, I can’t help but think the reason the whole taco bell equals poops thing is so prevalent is because of underlying racist sentiments, the same as with Chinese food and msg.