I will be sending a letter. I am also going to ask my father to get in touch with higher-ups at the American Dental Association, and see if they would be willing to avoid planning any conferences at Hilton properties. I don't know if they (the ADA) will go for it, but it's worth a shot. (My dad is a long-time member of the ADA and the president of our local dental association. He's also a veteran.)
FYI - The ADA they are referring to is the Americans with Disabilities Act, not the American Dental Association.