Prosecutors in Trayvon Martin case fight to keep Martin's toxicology report from trial

Why would a prosecutor think that it is reasonable to hide Trayvon Martin's drug use and violent history from the trial?  Violent criminal history is one thing, but what can you say to justify excluding drug use or texting at the time of the attack?  The texting surely goes directly to Trayvon's state of mind.  From WKMG Orlando, Florida:

. . . The state said in motions filed on Friday they want to prevent Zimmerman's attorneys from bringing up Martin's personal life, including his school records, previous suspension from school, fights, text messages sent prior to his death unless related to case and his social media use.
The motion also says the state wants to prevent the defense from using Martin's toxicology report, which showed the level of marijuana in Martin's blood the night he was shot and killed.
The state's filings suggest they fear the defense may try to attack Martin's character, instead of focusing on whether Zimmerman murdered Martin. Assistant prosecutor Bernie de la Rionda argued that Martin's past is irrelevant and would clearly be designed only to prejudice the jury. . . .