I read your reasoning for blaming the Nebraska staff, but I don't really see it that way. Being a South Carolina fan, you should know all too well that some players just make stupid decisions. Dennard is a great cornerback, as you pointed out. He always goes one on one with the opponent's best receiver, and he is usually successful. He didn't need safety help because I'm sure he saw the situation the same as we did - he gave up one big play, the Hail Mary was luck and the rest of it was Dennard doing a pretty good job.
Your other suggestion is purely conjecture, because you don't know what the Nebraska staff was doing/saying on the sidelines. Maybe they said/did all those things you suggested, and Dennard still lost his cool. How many times do you think the SC staff told Stephen Garcia to get his act together, yet he continually made the wrong choices. By your definition, I should assume the SC staff did nothing to prevent Garcia from making stupid mistakes and eventually getting kicked off the team.
I know your opinion is well-intentioned, so just know that I'm not attacking you. I just don't see it the way you do. Players are ultimately responsible for there actions, and even the best coaches can't prevent players from making stupid decisions. It happens.
Lastly, I think Blackmon is going before Jeffrey, but I've also seen Blackmon play a lot more this year.