I don't have a problem with the announcement. I think many people are too precious.
Warning about sniffer dogs at domestic airports is part of the standard announcement, the cabin crew member simply went a little further, perhaps as a joke, perhaps by way of warning.
Do I think the majority of festival goers are criminal drug traffickers? No.
While not condoning the use of drugs, not all episodes of drug taking end in the tragic circumstances a lot of people believe they do. Some people are addicted to drugs, and the same as alcoholics, they need help, not criminal punishment. If you do something wrong under the influence - throw the book, but that's not what we're talking about in the vast majority of cases.
Should all cabin crew be made to go to hospitals and rehab centres to see the effects of the alcohol they serve on board?