Lets face it: lowering the alcohol limit lower than 35mg/100ml may crimilize someone who has just washed there hands with alcohol at a hospital and will not serve a stronger deterent than actually increasing the penalty. Most incidents that occur with drink drivers are twice over the limit which means that lowering the limit will not bring these incidents down because these drink drivers did not care about the limit in the first place. They were only bothered about the probality of getting caught and the cost. Increasing the penalty will act has a stronger deterent at the expense of leniency which gives drivers an ultimatum.
Doing it this way would send out a message that drink driving is not tollerated at the expense protecting someone who had a sip of beer as the penalty would be unethical for that person.
The bottom line is drink drive penalties need massively increasing without putting penalties on someone who more fit to drive than someone who is slightly tired.