I am a little uneasy about the lengths of sentences as well, for two reasons mainly.
Firstly, the sentences look a bit too much like "the heat of the moment" or rough justice.
I do understand the public's anger and the view of the courts, it just may not too well in a year's time looking back. Also, there is the positive deterrent effect, to discourage others for acting in a similar way in future.
Secondly, the courts are operating 24 hours a day and at some time the future, an appeal court judge may rule an "unsafe conviction" or coercion, to previously made guilty plea. Say, example, if some yobbo calims he was forced into pleading guilty at four in the morning.
EDIT: For clarity, I would not want even one of these f**king sociopaths to have their conviction quashed at a later date and then be able to claim compensation.