From following along, this topic has struck some nerves...
As science advances and more things get packed into the things we consume on a daily basis, there are going to be more and more reactions occurring. It's not just limited to peanut butter. All of these medications people are on for different personal problems, experimental treatments and such, they ALL have side effects. Some cause you to maybe gain weight, others may give you an allergy you didn't have before. Our bodies also change as we age, again, leading us to be allergic to things we weren't before.
Should the airlines ban peanuts? That'll most likely be for a court to decide. There will probably be scientific studies brought in as to what the top food allergies and such are and it'll get messy and take a long time with appeals and such. The airlines are doing what they can and want to right now, but that could all change. It would be nice that if the person with the allergy makes it known early enough to the airline and the airline can spread the word of a peanut free flight to fellow passengers, then maybe that kid who needs that PB sandwich can eat it BEFORE HE GETS ON THE PLANE (and then subsequently clean up and wash his hands). Giving the kid his PB fix for his issue and then the allergy flyer also has their end taken care of.
When it all comes down to it, the person with the peanut allergy is asking for help and trying to inform. If you are traveling with someone that has other issues, reach out to the airline. Of course not everything will covered, but hey, it never hurts to ask, right?
The phrase "what's the worst that could happen?" comes to mind with all this. Well, if that's you who says that and you see first hand the problems it could cause, maybe your outlook will change. Could you live with yourself if an announcement was made to refrain from simply eating anything with peanuts, you didn't honor that request and you were delayed or missed a connector or saw a person die or nearly die because of your ignorance? Probably because you'd (generalization, not singling anyone out here) be too absorbed in being upset that your vacation was ruined because of someone else's problem, yet you didn't realize you were the cause of it.
To those that feel they don't need to heed the simple requests like this, I hope that somewhere down the line, you don't need to rely on others with a similar request and see/feel/experience what these people go through.