The devil, as always, is in the details. Was this a friendly disagreement, like whether the Dolphins were going to suck this year, or a violent outburst, like "come out here so I can kick your ass"? Considering the outcome, I would suspect the latter, in which case it's a justified shooting (and a good law).
"In June, unarmed Jason Rosenbloom was shot during an argument in Clearwater with his next-door neighbor."
"Well, he should have armed himself." - William "Bill" Munny