The real question is "How drunk is too drunk to give consent?".  After a drink or two most people are still able to make sound decisions.  After that it starts to get fuzzy.  Maybe excessive alcohol consumption isn't such a good idea.  When a person's state of mind allows them to feel that it's appropriate to get completely smashed what other irrational decisions might they make?

The cab driver was definitely not a very moral person if he had sex with an inebriated woman but if she actually did for some reason give consent he was still within the law, which is probably due for an overhaul so that good morals are imposed on people who are otherwise lacking.