Thanks for the input, april, Trefor, and axis. You're right. After I read everyone's take on the issues with which I'd been dealing, I believe now that much of the problem is with my in-laws rather than with the broader culture in general. I mentioned in one of my replies that I just kept being told that everything I observed was just "the way things are done here", and that's what gave me the impression that the issues were cultural. Thankfully, I know now that "here" doesn't necessarily apply to most people. I'd been looking for context and input from other parts of the country, and that's exactly what I got on this forum.
The funny thing is, I do actually get along with my mother-in-law. The frustration built up for me because as sweet as she is, I always end up trying to sugarcoat things when I talk to her. At the moment, she has absolutely no idea of the horror I've felt for her food or her crazy ideas about making pregnant women sick. I've found a work-around anyway. Every time we eat at her house these days, I follow her into the kitchen "to help" and make sure I prepare my own meal.