THE WOMEN TOOK THE DRUGS WILLINGLY AND WENT UP TO HIS HOTEL ROOM.
The drugs gave them amnesia so there is no way to know if the ladies later changed their mind, so legally they can call it rape.
He did not secretly drug their drink, which is what usually happens in rape cases.
Nobody is taking Quaaludes to make anything "more exciting". They're a powerful sedative, not a stimulant.
This is simply a paper thin alibi.
Even with criminal immunity he didn't want to openly confess the real motivation for drugging his victims.