So you would argue that someone who kills someone in self-defense should be treated the same as someone who pre-meditated their killing? As you would say, that would be “a distinction without a difference, in practical terms.”
I don't think that analogy holds up.
Murder and killing are not the same acts, necessarily, and killing in self-defense is certainly not the same act as murder.
Driving impaired is driving impaired, regardless of the substance.