Stealing implies that the theft of the "thing" denies the original owner of possession and use of that same "thing".
Digital IP is different - you can make infinite copies of it. A copy I make does not diminish your copy, nor does it deprive you of possession of your copy, or usage of that copy.
What it does deny you is the amount of money which you might have made on the sale of that copy (if you are the rights-holder and are selling the digital IP "thing" to others). I haven't, however, stopped you from continuing to sell your digital IP "thing" - you still have it. You just don't have the money.
Surely you can see this difference? If it could be called anything, it would be considered theft of opportunity, rather than theft of an object. You have been deprived of making a portion of money.
Now - that's very close to - if not almost identical, to me going up to your digital IP (via website, a kiosk, you at a table burning copies onto disc - whatever), looking at it, then saying to you "I would love to have a copy of this, but you know, I just won't, because you are charging money for it".
I still haven't deprived you of your IP - you still have it, you still have your copy, etc. What I have done is deprived you of the opportunity of making money. Should I go to jail, or be fined, or be forced to pay you the money in some manner because I didn't buy it?
The only real difference between the two? Well - in the first scenario, I have a copy of the digital IP; in very real terms, I have the knowledge of a particular number (because that is what any digital work can be reduced to - just a very large number) - in the second case - I don't.
But - what if on the off chance I somehow guess that large number? What if I am able to do that? Since it is a real number, there is that possibility (granted, the probability of being able to do so is vanishingly small). I know have the knowledge of that number, and can use it as I see fit - including decoding it to watch it as a movie, or play it as a piece of music, or whatever. But I didn't copy it from you; in fact, you might not even know that I now know your number!
Have I committed a crime?
DRM (and the laws which surround it) - in a very real sense - is a system put in place to criminalize and prosecute people for knowledge of particular numbers - nothing more, nothing less. In other words, knowledge of such numbers is considered a crime, unless you have paid money for that knowledge - even possibly if you independently arrive at that knowledge.
Agree or disagree - but it's the truth.