I wonder if it's something your body has to get used to? Raw milk has been rare in America for quite a while and I doubt these lawmakers grew up on it. Certainly people drank it for thousands of years and if it was something that had a very high chance of making you sick every time then the practice of drinking fresh milk would have been abandoned pretty quickly and drinking milk would be about as common as eating raw chicken.

People aren't dumb: the Inuit knew to leave polar bear liver well alone and the Mesoamericans knew corn had to be nixtamalized. Another example would be how cassava has to be washed and soaked in a particular process. There are many examples I can think of. Even if the actual mechanism behind these things wasn't understood until modern times people across the world still figured out "you must not eat this part" and "you must do X, Y, and Z before you can eat this" for a lot of toxic or potentially toxic foods.

I'm no expert on foodborne pathogens but it just doesn't make sense to me that people would drink something that would almost certainly make them sick. It seems to me it would be more like, say, eating eggs over easy: it's a risk to be sure but you'll probably be fine if they're fresh and the chicken was healthy.