I personally see this as being equivalent to a courtesy lock on a bathroom in a house. By default, if someone clicks the button on the knob, anyone else trying to enter the bathroom cannot, because the knob won't turn. But, grab a toothpick and "pop", the doorknob is unlocked.
There can be a great many reasons why someone might want to force their way into a bathroom (the vast majority of them having to do with emergencies). In general, it's to handle circumstances unforeseen by the person who set the lock.
The same goes here. Someone sets a lock on a PDF, and it's an advisory measure. (If it really, really mattered, they would have encrypted it.) The lock says "Hey, I don't think you should copy this." It's an advisory mechanism, though, and easily bypassed. And that's how it should be. The person bypassing the lock at least has a chance of knowing the intent and desires of the author.
If I were to propose a change, it would be this: Convert the "DRM says you cannot do this" dialog that has a global, sticky override flag stored elsewhere to a "DRM asks that you not do this" dialog that has a per-instance override button that says "Copy anyway." That way, the user at least gets informed of the author's intent, even if they choose to override it. Overriding is easy, but not so easy that the user never learns of the author's desires. If you want to get fancy, remember the decision per-document, but don't make it global by default.
The current mechanism of simply disabling DRM checks across the board would be equivalent to banishing courtesy locks on bathroom doors in my analogy above. It totally disables and removes the mechanism provided for stating intent.