Ah now that is not clear to me from the post - it sounds much more the seat than whether one was available or not - to the point that you missed a flight because of the seating.

I would also say that had the gate staff got security or the police to off load you I would agree. Any event what the hell do you care what anyone else on board the aircraft thinks? When they pay for your ticket then concern yourself about "them" and what if anything they think.

About the matter of the offloan I think that you are on firmer ground. Why would they offload you at that point? Why not just move you - Ground staff do it all the time.