For me, the reason I'm not a big fan of drafting RB's high in the first round is the usage of them in an NFL scheme. In many cases teams are rotating backs by committee. Another reason is the lifespan of a running back is lower than any other position.
Now, if a team is going to draft a running back and make him a feature three down back, then I have no issues with drafting a running back because he will also touch the ball more than any other position outside of your quarterback.
I'm a fan of Derrius Guice, but he hasn't been used much in the passing game at LSU and if we don't think he can be used in the passing game, then we should be looking for a back we are more comfortable playing our 3rd down back role, instead of using our 16th pick on a player we feel will be playing 1st and 2nd downs.