People speak so lightly about someone committing a murder and just getting 15 years w/plea bargain and that's all. Hate to break it, but over a decade in prison is not exactly something I believe most people take lightly. In states where the death penalty is present, homicide rates are not significantly different than states where it's abolished. There is a point where it wouldn't really matter if the maximum sentence were 20, 75 years, or the needle... very few would really be willing to risk so much to kill someone else.
I would be for sentences not to be served congruently for serial killers or rapists because they already demonstrated that they continued after their first victim. Some people are so mortified after killing once that they wouldn't have committed the same act again. To those people who act twice or more, then I would support life w/out parole; but only because they didn't have enough remorse to stop. For those who acted once, there is the possibility that they have already changed. Those such people should serve a decent chunk of time, but there should be the option for parole at some point.
That's not 'get out of jail,' it's a potential incentive for people to change. Those that don't would be rejected.