1. Personally have absolutely no problem with that, don't see how keeping him in for longer would make any difference.
2. Do you really think there's any chance of recidivism in this case or indeed any case when a previously functional member of society does something stupid behind the wheel resulting in death?
3. You would, because even in countries with the strictest laws, people still make huge errors of judgement or just don't think they'll get caught. You want to give a life sentence to "every person who kills or injures anyone through a deliberate action" which includes speeding, running red lights, etc which happens to a greater or lesser degree literally everywhere. You'd also have to vastly increase the penalty for mistakes such as failing to look properly when pulling out of a junction and killing someone to bring them in line with your proposal, further increasing inmate numbers.
Look at states in the US with the death penalty or indeed idiot Europeans who try to smuggle drugs into / out of countries where death is preferable to entering the prison system. Despite the consequences being much more severe than in the UK, people still get do it.