Why would the body include congenital defects of any kind? Bugs and duplication errors that didn't produce useful results. One mutation or genetic development might lead your body to be predisposed to overreact to otherwise harmless allergens; a similar mutation might ramp up your immune system so that you're less vulnerable to fatal diseases.
Don't anthropomorphize evolution; it has no intent, and does not actively "select" beneficial traits. Over time, whatever traits happened to propagate will propagate. Some of those will be beneficial; others just didn't happen to kill people.
Notice that there's no widespread anaphylactic-level allergy to, for instance, water, or some standard component of atmosphere. But an allergy to peanuts does not systematically kill everyone who has it before they can reproduce.
I'm not referring to evolution or defects here unless you're implying that it is a defect that our body would willingly choke itself to death in reaction to an allergen (I agree that it's probably a defect that we react to the allergen in the first place)
Exactly that. Your body has a defect that causes it to choke itself to death in certain circumstances.
And thanks to the evolution, if not for science, the defect might be eliminated in a few generations. Or not - perhaps this is an optimal variant of immune the immune system. That is - 90% of organisms will have an excellent immunity, but it will go haywire in 10% of cases, whereas an alternative would be a system with 99% organisms having just an average immune system, but 1% being haywired.
Finally, evolution has no "target" or "goal" really. Some features will be broken, and some will be useless. Some may serve a purpose that's beyond our understanding or extremely complex.
Don't anthropomorphize evolution; it has no intent, and does not actively "select" beneficial traits. Over time, whatever traits happened to propagate will propagate. Some of those will be beneficial; others just didn't happen to kill people.
Notice that there's no widespread anaphylactic-level allergy to, for instance, water, or some standard component of atmosphere. But an allergy to peanuts does not systematically kill everyone who has it before they can reproduce.