He was not enforcing the law. He was lawfully expressing his discontent. I can tell someone when they've done something that is shameful and unacceptable. He shouldn't be at risk of death from being pushed down onto the pavement just because he verbally expressed his discontent.
From another point of view he was an armed stranger who began to verbally acost a woman and her kids with enough rage that it caused on-lookers to run into the store to inform management about the altercation.
He has no right to disturb the peace. And if I see someone threatening my family I’m inserting my self between them and him.
In fact, since police are taught to assume both parties are armed in any altercation it would be reasonable to assume he’s armed (which he was) and fear for my life and the life of my family.
If it’s Florida and I’m armed I can legally shoot him under those circumstances.
This father was unarmed so he had to surprise the instigator before he could harm his family. In this point of view he died defending his family from an armed man.