Being armed isn't directly connected to who initiated the confrontation. It'd be one thing if Zimmerman confronted Trayvon with his gun drawn. However, the gun came into play after the physical confrontation happened. A "reasonable" juror would want to know who started the physical struggle, and under what circumstances the gun became involved while under Zimmerman's control. So if Zimmerman's story is that he didn't throw the first punch, and after the fight started getting out of control he legitimately feared great bodily harm and that his life was in danger, then the sustained injuries, the inconsistency of the witness' statements of residents in the complex regarding the fight, and the fact that other than Det. Serino's initial report, the Sanford police did not charge him and bought his story of self defense provide a fair amount of leeway as supporting evidence of that claim of self defense.
To your second point though, while I personally feel that Trayvon was profiled, followed, harassed, and murdered in cold blood, that has absolutely nothing to do with the possible potential for Zimmerman to get off, so while it would be easy to merely speak angrily about how much I want Zimmerman to get what he deserves, and echo all of the news that trickles in about how much of a liar and manipulator he is, and emphasize all of the details about the case that support why it's a slam dunk and why we should just skip to the sentencing phase and pencil in the guilty verdict by default because it's a no-brainer...the fact that he could get off means I'd rather speak on the case from an unemotional and unbiased perspective, and look at potential arguments and defenses that could be used once the trial starts.
The random opinions of people on a message board about the Trayvon Martin case ultimately are all conjecture anyway, so if me speaking about possible legal approaches that could be used by the accused is "cheerleading"...then rah, rah, rah, breh...