"This is America," you say, and the system is racist. But Zimmerman is not "the system." He's not the New York legislature (or even a New Yorker). He's one man, and a racial minority at that. Arguing that the justice system's sentencing has a disproportionate impact on African-Americans or that New York has a law that's imposed in a racially-discriminatory way does NOT mean every single person who lives here in America is racist. It does not prove that one man, a Latino in Florida, is racist. And people are stating that Zimmerman must be a racist SOLELY because (1) he's American, and (2) he was involved in an altercation with an African-American young man. I'm not discounting the possibility that Zimmerman might have been racist, but I take severe issue with stating it as fact when there's zero supporting evidence, and plenty of evidence that Zimmerman himself is not racist.
Slate, a liberal and anti-firearm publication, ran a piece after the trial admitting that there was no evidence of racism by Zimmerman and much of the impressions people had of the incident were due to poor reporting early on and were not backed up by evidence at trial:
http://www.slate.com/articles/news_and_politics/frame_game/2013/07/trayvon_martin_verdict_racism_hate_crimes_prosecution_and_other_overreactions.html
Also relevant as to Zimmerman himself (not America overall, not the American justice system, but Zimmerman the individual), the FBI has done an investigation and found no evidence of racism:
http://www.cnn.com/2012/07/12/justice/florida-teen-shooting
As for the confrontation and your assertion that Zimmerman started the physical part of the altercation, consider the physical evidence. Zimmerman had injuries to his face and to the back of his head. He did not have injuries to his hands or arms. Martin had injuries to his knuckles, the gunshot wound (which forensic examiners stated was consistent with being fired at someone standing over a grounded target, since the sweatshirt shirt was 2-4 inches away from the skin at the time the gun was fired), and no other significant injuries. If Zimmerman had swung first, wouldn't Martin have a busted-up nose or the like? If Zimmerman had been holding the gun on Martin before the physical altercation, do you (1) think Martin would have rushed him (not many people run at a gun), and if so (2) do you think Martin would have concentrated his blows solely at Zimmerman's head instead of trying to wrestle the gun away? The fact is, Zimmerman's story is the most consistent with the physical evidence.
As for the argument about it being impossible to draw a gun when someone is on the mount, you're assuming that Martin had a UFC-perfect mount and that the holster was exactly at three-o-clock. Neither of these are safe assumptions. If an untrained individual is straddling another person while hitting them in the head, their mount is not going to look like a BJJ black belt's, and easily could leave room for someone to pull a handgun.
Ask yourself one question: if Zimmerman was planning on murdering a black man, just shooting Martin because he was black, do you really think he'd have called the police BEFORE he did this? Of course not.