The murder v manslaughter debate is exactly as thegreatape states.
there is Manslaughter by raising a special def (diminished responibility, provocation or suicide pact) there is manslaughter by an unlawful act or manslaughter by gross negligence.
In the 2nd - manslaughter by an unlawful act , they have conducted a positive act that caused the victim's death and was inherently unlawful, such as punching someone who falls backwards and hits the pavement with his head and dies.
Murder is the unlawful killing of another human being under the Queens Peace with malice aforethought (ie with the intention of killing or causing GBH).
however in both offences you will be aware of your actions! Manslaughter saw the risk and went onto commit the offence anyway.
I can say that if I got sent to prison it would send the holy bej***out of me and I would not be committing any further offences, however the kind of people who are "in and out" of prison are normally those that have no house, no income, no job (okay normally because of their own volition) but prison to them is an easy ride, 3 regular meals a day, access to a gym etc etc.
For the law abiding citizen I think prison is a deterrent.