Where to start?
First off, he was not in violation of the contract. The contract says that a seated passenger can only be removed for one of 19 different reasons, i.e. drunk, rowdy, smelly, blind without a guide, etc.
Needing your seat for another employee ain’t on the list, and United has admitted this.
The ‘police’ were not called. These were not police. They were unarmed security guards. They have no right to issue ‘orders’ to anyone. Other posts have indicated they didn’t even have a right to be on the plane at all.
The 3 suspended airport security officers wrote reports laying the blame on Dr Dao for his injuries. However, 2 of those officers prefaced their report with the claim they wrote it under duress and only to keep from being fired. The officer who slammed Dao made no such disclaimer. Very odd. Their reports can be seen here =>
The meta-lesson for me is never patronize a company run by a Mexican.
There, I said it.
Needing your seat for another employee ain’t on the list, and United has admitted this.
I think that is a point that would have to be adjudicated in court. You are relying on the word "overbooked" and we all assume it means that too many tickets have been sold or some such, but so far as the legal argument of the airline industry may be concerned, it could mean any condition in which they have too many passengers.
Then there is the matter of the agents acting in good faith. So far as they understood the term, they were "overbooked". Even if their understanding is wrong, Dr. Dao should have complied with their requests for him to leave. He should have litigated his case in court after the fact, not by refusing to comply with what the flight crew regarded as lawful orders.
The ‘police’ were not called. These were not police. They were unarmed security guards. They have no right to issue ‘orders’ to anyone. Other posts have indicated they didn’t even have a right to be on the plane at all.
The reports I have heard were that they were Airport Police. A quick search reveals dozens of articles claiming it was the Aviation Police of the Chicago Police Department. Here is just one.
https://www.dnainfo.com/chicago/20170424/ohare/united-dragged-plane-david-dao-aviation-officers
They have no right to issue ‘orders’ to anyone.
I think that will depend upon whether or not they were really police officers. From what i've found on a quick search, it appears they were, and therefore were able to issue lawful orders with which Dr. Dao refused to comply.
Other posts have indicated they didn’t even have a right to be on the plane at all.
You can rely on "other posts" if you verify the material from authoritative sources. People on the internet can say all sorts of nonsense, and until you find out for sure, you can't rely on "other posts" to prove something.
If they were members of the Chicago Police department, or some other legal authority, then they had a right to be on that plane once called by the flight crew, and your "other posts" are just wrong.