You sure that won't get you into trouble?
As long as your not writing legal opinions you should be fine, affidavits are for facts. The writer is simply testifying that he/she is in fear of the IRS and only complying for the sake of preserving freedom/life.
The IRS fined a guy (this was a long time ago) for writing "under duress" in the notes section on his check. I don't recall the details of the story (though now I'm gonna look it up), so I don't know how they got away with it. But it's worth remembering, unless you think you'll have a LOT of people sending it in.
DO NOT attach to your return, this may result in in more theft.
If it is attached to your return they can claim something like "frivolous return" and fine you 5000 dollars.
You could put into the same envelope but it may be better just to send in a different envelope.
Or even better, serve it to them face to face at their fortified compound. Get a recording and put it on youtube.
I will just be mailing one in and/or calling them the question the agent.
American officials do seem to have an appallingly bad sense of humour. I once had the temptation to write "yes", on a plane to the US, to this truly idiotic question on the tourist form asking whether I was a war criminal or some such rubbish. I'm glad I didn't, because I heard, later, that some other tourists had done that as a joke on previous flights, and had been duly forced to fly back on the next plane.
True. They are super serious, but who else could do such a job. None other than a complete fool whom buys into the fictional social structure 100%. High stress people who do watch too much TV and then compound more stress working in the positions that they do.