I don't follow the celebrity gossip, so I may have got some of the details wrong, but…
Mel Gibson's ex wife recorded some potty mouthed phone calls he made to her which included some rather unpleasant racial comments.
As a result, his film career is pretty much over.
When's the last time you heard Gary Glitter or Jonathan King on the radio ?
They have become unpersons because of their crimes.
Many celebrities get arrested for drug crimes and it is accepted as normal behaviour. A bit like speeding, everyone does it, you're just unlucky if you get caught.
A short spell in rehab and they're on to their next film or record contract.
I'm not saying what should, or shouldn't happen, but if they* were serious about stopping drug use, they have the power to do something far more effective than fines or short prison sentances.
*"They" in this case is the media and entertainment industry.