That's fine. Let's all forgive drunk drivers, they just want to get home, no matter how much carnage they cause. It's a stupid phrase that enables all sorts of black stupidity.
You've taken it a half-step too far, but yes; if you assume that drunk drivers are, in fact, not setting out to comment manslaughter, then you can see what causes it and push for taxis/uber and actually get people off the road. Or you can assume malice, demonize them and end up like MADD.
I like to modify it and call it Hanlon's Scythe:
"In the absence of clear evidence, don't automatically attribute to malice, that which can be trivially attributed to any other cause"