I completely disagree. If she's acting irresponsibly and engaging in risk taking behavior, it is absolutely his prerogative and duty to tell her to not do that thing, with those people. He needs to keep her safe. Going to bars, engaging in illegal activity, and affiliating with hard drug users is not safe.

That said, OP, you might want to consider doing one or the other with her. MDMA and cocaine produce a similar high. You would be surprised how much control you have while under the influence, because these drugs work by increasing focus to a ridiculous degree. The reason I'm encouraging you is because these drugs aren't scary if used responsibly. How else would you learn about responsible usage unless you try it?

The worst part of the experience will be coming down, so be prepared for feelings of dread and anxiety the day after. You'll want to do the research on addictive effects yourself, but from my experience, I've never felt an urge to go back to coke. Of course, I've had experience with ADD medication (think Adderal) previously, so I already knew that sort of high wasnt my thing. The real addiction comes from your social circle and habits. To cut the drug, you need to cut the people who enable that lifestyle.

The scariest part about MDMA and coke is the people who sell it, closely followed by irresponsible and out of control users. There's alot of money in these powders. Alot of risk. They're frequently gun owners, and for good reason. The middlemen you deal with are usually the friendly talkative sort, though.

To sum it up, get on her level. If she's going to be at bars/festivals, doing drugs, you need to be there with her to keep her safe. If you won't accompany her, leave her, so she can be with somebody who will protect her from rape. It would humanize her if you experimented, this is a person and your GF.