Again, clearly a mistake on Grosjean and he deserved the penalty.
But what is a fair penalty? Taking out world championship contenders will be race ban? and taking out mid-field will be 10-place grid penalty? taking out drivers never scored any points yet will result a 3-place grid penalty? Victims will be accumulated penalties?
Perhaps the stewards decided his mistake could result a very serious accident and injured some other drivers. Thus this kind of harsh penalty. But the thing is, (compare to Maldonado), Grosgean is very apologetic to the accident he caused and take full responsibility like a man. No excuses, just a bad move and over ambitious.
Unlike some drivers who never learn from his over aggressiveness, lack of driver respect and etiquette. Use his car as a weapon to crash on to Hamilton last year in Spa, and earlier this year in Monaco with Perez. These are the deliberate actions that can possibly injure other drivers, and these are the race bans that the stewards should given.