Because men are arrested for drugging women and sleeping with them. Regardless of whether the sexual act is committed or not, if a guy was caught drugging a woman he would automatically be arrested and charged and in some states it's a felony.
In my mind what Lois did to Clark is no different than a guy in a club slipping a defensless woman a "Date Rape" drug. Regardless of whether she thought Clark would not sleep with her the intent was the same, pure and simple.
