Sure, you eat thousands of things. But surely you're consuming less prescribed medicine. The onus is on you to read the material given to you when prescribed potentially life threatening medication. It's prescribed and not over-the-counter for a reason. There's extra precaution placed on the medicine itself, and so you should pay attention to that and read up.
More seriously, it is easy to overlook the extreme spectrum of knowledge and ignorance in our society. There are other factors too, such as cognitive impairment, state of mind, etc. Ignorance may be a poor defence under law, but in a more ideal world, ignorance of grapefruits shouldn't result in capital punishment.
With the extreme liberalness we accept advertisements everywhere, it doesn't seem unreasonable to dedicate an extra amount of space here and there for friendly warnings.
Edit: I see several comments stating that such warnings are printed on labels. If so, discard my comment. Other than verbal warning, that's probably adequate for our imperfect world.
Maybe you eat thousands of things and some interact with each other. You don't know, you're just hoping it will be fine, because learning everything about everything is not feasible, which was my point.
My secondary point is that everyone on this thread is blaming the victim for not doing enough research, while at the same time everyone on this thread is only marginally better - maybe you do enough research in this specific topic, but surely not for everything in life.