I am looking for the shortest comprehensive way to explain to people that are trying to use DRM as a technology to prevent users from using their data in some fashion deemed undesirable, why their solution cannot work by definition.

Ideally I'd like something that:

• Covers why technically it is impossible to have people access local data, but only in such-and-such a way
• Imparts an understanding of why this is, to avoid follow-on "But what if" rebuttals
• Is intuitive enough and short enough that even a politician (j/k) could grasp it

When faced with this situation I try to be clear and concise, but I usually end up failing at least on one of these points. I'd really like to have a 'stock' answer that I can use in the future.