"The primary problem with DRM is not only that it doesn't work, but that it irritates the hell out of law-abiding customers who only buy legal products (with DRM), but doesn't inconvenience pirates in the slightest. It's actually counterproductive. Customers learn to stay away from vendors of DRM'd products, once they've upgraded a device too far and discover that their old files are locked away from them and inaccessible (because the old software or keys won't run on their new gadgets)." -- Charlie Stross (a noted SF author)
I agree entirely, DRM is idiotic, doesn't work, and is counterproductive.
I'll wager most tech savvy leftists also agree with that thesis; because it's irrefutably and provably true.
But there is something else in that argument.
If you pull the logic out, and look at it apart from the subject of DRM you should see something.
The argument against DRM, is also the argument against gun control, and smart gun technologies, and for that matter, drug prohibition.
For each of those topics, the argument is provably and demonstrably correct. You can't refute them, because they are true.
You can dismiss them as irrelevant to the reason you support those policies; but from a practical standpoint, you can't be intellectually honest, and use the "prevention" justification for your support of prohibition.