@indigomoth - Not all allergies are caused by haptens, but some of them are. However, you wouldn't want to block them from joining to proteins altogether, because in some cases you absolutely want that immune response to an invader.
While allergies can be dangerous and certainly they are uncomfortable, they are a small price to pay for a system that generally does an excellent job at protecting us from dangerous bacteria and other body invaders that could otherwise quickly lay us flat.
Which is probably why it's so difficult to permanently combat allergies. After all, we know how to destroy the immune system.
Making it work just when we want it to work is a different matter.