"the logic is that being drunk makes the crime even more irresponsible and the sentence will be even more severe"
Actually this is interesting.
Take, for instance, killing someone by driving drunk. There are 2 ways of looking at it. The first (which is the one taken by our legal system, I think) is that they didn't mean to kill them, it was an accident, but one caused by their actions. This merits a lesser sentence than murder.
OTOH: The person chose to get drunk, and what happened from there on is a consequence of that choice.
They may be totally against drink driving when sober, but once under the influence their compromised judgement told them it was OK. However, they made the choice to get drunk, hence it is a consequence of their own choice and should be punished as a concious descision.
Then they hit someone and killed them. Once again, they may be a great driver sober, but killing that person is a consequence of their descision to drive drunk. It should be prosecuted as if they had made a conscious descision to kill that person, so should be treated as murder.
I am not saying that this is how it should work, nor that it should not be this way. It is just a very interesting thought experiment.