It's very simple. You refused to move to your ticketed seat, and refused to get off the aeroplane when ordered. Like it or not, you don't make caveats on the requests/orders of the airline staff, such as "only if you put it in writing". Neither should you. Therefore, by insisting pointlessly that the manager put it in writing, you were essentially not complying with his/Captains orders. Therefore, you needed to be removed. The cabin crew aren't going to manhandle you, the ground staff aren't, that's the police job. If you've flown to over 60 countries and crossed borders and started schools and written best selling books in a week yadayadayada, then you should have the A) travel experience to know that the seat on the boarding pass is the one you sit in, B) intelligence to realise that if you screw around on an aeroplane, you'll be meeting the local police, and C) enough knowledge of airline ticketing procedures and check in etc to realise that a hand written receipt with first class scrawled on it does not constitute proof of having purchased an upgrade.
It's certainly proof that someone has hand written first class on a receipt.
In addition, from your travel knowledge, I'm sure you'd be aware that access to the first or business class lounge is not evidence of having purchased an upgrade. There's lots of reasons people are granted access to the lounges.
Perhaps, for the avoidance of doubt, you'd scan your boarding passes and hand written receipts into the site so we can all assess how genuine they are for ourselves.
You could also tell the flight number and date, so we might check that there actually was a first class, in the interests of credibility.
For my money, I think you're more than likely that guy that has to make a scene, in a bid to validate himself and convince himself of his world changing ability.
As for your letter to the publisher on your website: if you'd written me that letter I wouldn't have crawled out of bed to reply to that obnoxious drivel either.
All the best