Dear Company Spokesperson,
Thank you so much for your response to the inquiry as to whether or not the ingredients in your product contain corn. 
I have to point out, however, that you were not being asked to comment on the safety of corn derivatives for individuals with corn allergies.   Nor are you being asked to replace the role of medical advisor.  And if I took your advice to discuss every product I was considering placing across my lips with my medical provider, my medical provider would not have time to attend to any other patients.  That's why they suggest I do my own research.  As they advise every patient to do. 
Which is why you received a letter inquiring as to the origination of your ingredients. 
I'm pleased to hear that you know of no documented reactions to caramel color/citric acid/microcrystalline cellulose etc.  Unfortunately, I have experienced reactions under blind trial conditions.  These reactions were identified through the use of food diaries and helpful companies who were willing to share the source of their ingredients.  How else would I know why ascorbic from batch A made me sick and ascorbic acid from batch B didn't? 
I believe my doctor's response was "Huh, that's weird.  There are no documented cases of allergic reactions to these derivatives.  But if they affect you like this, I think you should definitely avoid them." 
Which brings me full circle to the problem at hand. 
Where were your ingredients derived?  I am asking for my health, not for the heck of it. I'm not asking for proprietary information.  I'm asking for sources of ingredients listed in your product.
If you don't want my business, simply respond that you don't serve people with unique allergies.  Don't quote the FDA's impressive quality control measures.  I presume, since you are still in business, that you adhere to their policies.  I don't really care about FAAN's policies since the top 8 allergens, as identified by the FDA, don't really pertain to corn.  But I do think that as a consumer, I have the right to know where products come from.  What country.  What plant.  And whether the plant originated as a seedling or a science fiction worthy science experiment.  

Thank you.

This letter was inspired by THIS post at Delphi forums.