No, they have a point. Propaganda of the Deed is a tactic not a strategy. Going in blindly with any and every tactic is just like an army going into battle disorganized. Likewise an individual action cannot fix a systemic issue.

States routinely use adventurism to crack down on dissidents. Look at Haymarket where they rounded up leadership, even when several members weren't there, and had them executed. It is very easy for Mass Media and the Police to manipulate public opinion towards their narrative and justify crackdowns. Worse none of it led to any real revolutionary action among the masses.

The death of a CEO is entirely vibes, aka Idealism, without a corresponding Materialism. I doubt the shooter was motivated by class consciousness or a polling of public opinion. A CEO dies and the world moves right along, just as Capitalism intends. The corporation will still deny claims at the same rate, a new CEO installed, and investors will get paid their cut. Capitalism recycles individual Capitalists all the time.

The only thing that will result from this individual action

Sure, if you ignore literally all the people talking about it, agreeing with it, being inspired to share comics and stories illustrating the depredations of the insurance industry, etc

So far the shooter has no mass movement. It's pure vibes. We need to turn this Idealism into actual Material changes. Very literally Praxis. My advice is the same: Get organizing, capitalizing on the legitimacy, and save the adventurism for a shooting war. We can start by pointing out all the evidence that United is shitty, and capture all this energy towards a mass movement that gives us actual material power. Time is ticking because people will rapidly fall back into their previous thought habits, and this will be just another shooting in America.