Totally this.
The airline is committing basic PR errors in keeping this running for more damaging news cycles. The longer it does this, the worse it is going to get.
The CEO needs to be out there - NOW - issuing an *unreserved* apology to the passenger concerned, and those who witnessed it, and that they have a team of people working on making amends. Not doing so is constitutes a continued failure of leadership and recognising that the buck stops with him when things go wrong.
The first step back is a large helping of humble pie.
He should apologize for UA's part in the matter. The law enforcement agency has some apologizing of their own to do, if they would be deemed guilty of excessive force.
UA likely broke some CoC rules, and that alone deserves an apology and healthy $$ compensation.
You cannot pin fault on UA for the guy's physical condition. Come on.