He may have good cause to sue NBC, but the fact remains that he shot and killed an unarmed minor under circumstances that are still somewhat questionable despite the physical evidence.

I say questionable only because there is clearly more than one way to discern and to interpret the evidence and the various statements by Zimmerman himself as well as witnesses.

The very crux of the problem in my opinion is that there isn't quite enough evidence or a witness with enough contact during the event to completely clear Zimmerman or to clearly show his guilt. His early credibility problems with his donations and the slightly different stories he presents cripple his claims for self-defense and must be considered.

because if Martin did actually came back to kick Zimmerman's butt

if Trayvon Martin did so, there are problems with the really easily traceable time, even more if we add the up the end of GZ's NEN call and the start of the 911 call that records the screams, and add the scenario GZ gives in his reenactment.

I disagree with BTD as he (I keep saying he, but perhaps it is she), seems to think that what NBC did is not wrong and they should not be sued for it (or that Zimmerman will lose or not get much of a settlement... who knows).

He's saying no such thing, which I presume is the reason for your qualifier ("seems to think").  He (BTD is a "he") is direct and to the point.  No need to try to read between the lines.

Above, BTD stated that it is a big assumption to assume Zimmerman is not a racist.  Based on the discovery, the fact that this is not being tried as a hate crime, and that the Feds have determined through their investigation that Zimmerman is not a racist, then BTD's statement is not factual.  This is much more BTD's opinion than based on any evidence that is known at this time.

What do you mean "not factual"?  It's his conclusion which, by definition, are "not factual".  This conclusion is no less "factual" than yours.  Moreover, BTD is not saying that Zimmerman is a racist ... he's saying:

1.  the mere fact that the DOJ investigators found no evidence to support the theory that Zimmerman is racist (or was motivated by racial bias or animus that night) does not establish that he isn't/wasn't.  

2.  By suing NBC for defamation, he puts the issue in controversy and invites the defendants to further investigate the issue.  Moreover, the types of information that would be relevant and potentially admissible in a civil suit are far broader than could be used against him as a criminal defendant.