One could almost say "Why does it matter how much they drank? The children were left out of sight and hearing - end of. The question of drink only adds to the lack of responsibility.
The question of drink came into it because drummer asked "If the Mccanns had decided to stay in the apartment that night and drank alcohol, forgot to close the doors/windows or failed to secure the place etc how would you feel then CPN?" and I answered that "If, as responsible parents, they drank so much alcohol that they forgot to lock up properly, then yes, that would be their responsibility." The matter of responsibility remains.
As I said in an earlier answer:
"We are all, in the last analysis, responsible for our own actions - and that applies to parents who leave their children alone out of sight and hearing, drivers who speed, drivers who drink too much etc etc.
And we are then responsible for the outcomes of those actions"