I suppose at some point it might be called stalking if you did it regularly to someone, but that is obviously not the case here.
Zimmerman is a free citizen, and as such had no obligation what so ever to listen to the dispatchers advice. If he refused to listen to the dispatcher and kept following Martin.. was he dumb? maybe so. But that is a far cry from saying he somehow committed a crime by continuing to follow Martin (assuming he did so)
It's not so black and white as you have tried to make the case above. Threatening actions or words can be considered battery. If there is any proof that Trayvon could have reasonably been in a position to defend himself, and the confrontation was instigated by Zimmerman, than the aggressor of the confrontation has culpability, regardless of the outcome.
You stated earlier that it does not make any difference who starts a confrontation. You say it only matters who was defending themselves at the end of the fight. This is absolutely wrong. You cannot go into a bar, call a redneck's girlfriend a slut, punch the biker boyfriend in the nose and then start shooting when 4 behemoth bikers begin to tenderize you. That's manslaughter.
This case is complicated. I have gone both ways trying to sort it out. I can't find evidence (that is published) suggesting Zimmerman should be arrested. But he is the only living witness that could draw a complete picture.
That said, the whole Sharpton, Jackson, racial and now political aspects of the case are clouding the ability to have rational discussion about it. I do not see anything in the evidence published that suggests a hate crime.
But I am now leaning toward Zimmerman being a cop wanna be. Though I'm not sure that affects the case beyond a state of mind and likelihood that he may have instigated the confrontation.