Cognitive dissonance is a thing, yes. Would you also be surprised to know that some Americans smoke and don't use seatbelts?

Not every immigrant is a twenty something working on a Masters degree or working in the tech industry. Most of the Bengalis I know, especially in the NYC area, are here by sheer luck and determination moreso than formal education. The older ones have survived famine, cyclones, and literal genocide. At that point, trying to convince someone that their favorite spices or sweets that they grew up with for 40+ years may be harmful is pretty difficult.

If anything, getting to know the immigrant community has been enlightening in pointing out my own biases. It's easy to point the finger at someone else because they're a fish out of water. But put me in a different culture (or really just let time pass with the attendant changes in culture and technology) and the same thing would be true for me.

Contaminated spices they have grown up with, yes. One of the insidious things about lead poisoning is that low levels are not that apparent when looking at an individual but still have a significant effect - you wouldn't know if you are less intelligent than you would be without exposure.