Sending letters is a great idea. I'd make the letter a lot shorter though - basically 3 paragraphs, 6 sentences.

1 I'm canceling business trip to STL. [you don't need to point out that you would have spent money, it's obvious]

2 I have decided to avoid air travel because of TSA security procedures. I believe that TSA "nude" body scanning and intimate touching of private parts is unacceptably invasive. As survivor of sexual abuse, I feel strongly about this issue (or leave it out as TMI). [/9/11, effectiveness of scanning, clothes, genitals etc, not really relevant]

3 I understand that even tho city owns the airport, it's not directly responsible for TSA. Purpose of letter is to help mayor/tourism officials understand impact on city and encourage them to raise the issue at higher level. [what you specifically want them to do]

These people are busy -- the goal isn't context or eloquence or rhetoric -- it's making the point as efficiently as possible.

Just my 2c, of course. The important thing is to write and ^ for taking the time to do it!