That's true but I don't think that is the point being made. No one is saying that Zimmerman violated a law by not identifying himself. But if we are going to try to reconstruct what happened, it's a meaningful point that goes to his state of mind.
If as a neighborhood watch volunteer he wanted to protect the neighborhood and he didn't know whether Trayvon belonged there, then the simplest way to find out would have been to ask him from the safety of his car, early on, and he didn't do that. According to the friend on the phone, he didn't answer Trayvon's question as to why he was following him. Why not? No, of course there is no law that says he should but in the first opportunity lost, he might have been able to reassure himself that all was well and continue to Target. In the second opportunity he might have defused a situation in which both people were clearly distrustful of each other.
I believe this is because he had already decided, in his mind, that just as he told the dispatcher, Trayvon was up to no good and there was no reason to consider that he was someone who belonged there minding his own business let alone think that he himself might appear to be a bad guy to Trayvon. In addition, his words about *advertiser censored**holes and punks show some anger IMO.
I believe this mindset that Trayvon was a criminal and his anger at others who 'always get away' set the stage for the deadly encounter. I believe that he was determined, not to see where Trayvon was, but to detain him to prevent him from getting away before law enforcement came. And I believe the detention was an illegal act.
What are your thoughts about why he failed to identify himself as neighborhood watch volunteer ( he need not have said his name)?
I could say that my opinion of him not identifying himself would be that he was more concerned about this individual harming someone or someone else's property. The fact that he didn't identify himself plays no bearing unless you're convinced of his guilt, and then you're just searching for reasons to justify your own conviction.