For example: Should a drunk driver who runs someone over get an equal punishment to that of someone just caught drink driving?
and: should attempted murder get the same punishment as murder?
In my opinion the answer is yes to both because the individual has done the same thing. If you get in your car drunk you know the possible consequences, just because you are unlucky enough to run someone over doesn't mean you should get a longer sentence than someone who gets stopped for weaving.
And just because a person is stupid enough not to pull off a murder doesn't mean they should get a shorter sentence. The person still requires just as much punishment/rehabilitation.