Sometimes, life is a bit more complicated than your remark suggests.
It really isn't. Sometimes people like to pretend that they're not responsible for their choices. That 10 years of helping old ladies put out their bins makes up for that one night of unacceptable behaviour.
Oh, they say, but it's so out of character for him to have done that. What rot.
What is an "otherwise good man"? Someone who generally most of the time doesn't do horrific things? What a meaningless construct - you are the sum of all of your actions, all of your choices.
That includes the choice to get into a state where you behaved badly even if you would not, whilst sober, behave in that way