No, he didn't nor did anyone claim that a crime was being committed. He was reporting what he saw as suspicious behavior.
so, he's now pursuing a person who is completely innocent of any crime. He ought to know, then, that the person he's chasing has no requirement to answer any question he poses, that any attempt to detain him will be a crime, and that he is now being provocative.
As I recall, the Stand Your Ground law doesn't require any illegal behavior, just provocative. So, by pursuing, Zimmerman is now the provocative party, and his self-defense claim becomes far stronger. However, since moving away from someone who is glaring at you is not at all provocative or suspicious in any way, Martin now has the right to stand his ground.
You only know no crime wasn't being committed because after the fact, we've learned that he was just a 17 year old boy visiting his father. Zimmerman did not have to luxury of reading all of this before he pursued the victim.
Then Zimmerman was being reckless. And actually, looking around and walking are not crimes, nor are they suspicious, but staring at someone and then pursuing them are extremely suspicious (in fact, it's downright threatening), and if his first words are "What are you doing here", then that's even worse.
How is him being advised relevant but not being advised suddenly doesn't make a difference? He was not advised, he was just told that they don't need him to do that, for his own safety, because at this point, police are responding to a suspicious, individual. At this point, the dispatcher doesn't know that it is just an unarmed 17 year old boy, looking for his father's girlfriends townhouse.
Not having advise doesn't mean that you aren't being reckless, simply put. However, ignoring advise from a professional, without having a strong reason to do so, does make it more clear that you are being downright foolish. In other words, he did something reckless, and ignored third party advise that he was being reckless.
If he didn't feel, know, or have a reason to believe he was going to use his gun, how is he to even consider that a death is likely? The gun may have been incidental at this point. He may have just had it on him when Martin ran and he chose to follow.
Because he was provoking a fight, the fact that he also brought a deadly weapon into the confrontation means that he bears at least moral responsibility for if it's used. And since he's the one that used it, after provoking a fight, he bears responsibility for the consequences.
Add to that, he seems to have lied to investigators, who themselves seem to have done a very bad job both of investigating, and of managing public relations (actually, they've been disastrous at PR). Yeah, I'm not surprised to see this amount of anger on display over this.