That's not the only difference: when you lend out a physical movie, you can't watch it any more. And even in cases where copies are legal, the other differences you describe are pretty significant. The only reason lending out things like this is legal is because it has natural limitations; limitations that don't exist with file copying.
Again though, if it's stealing according to natural law as opposed to just pen and paper then it would need real life equivalents.
The analogy that i used is repeating a joke to your friends which someone else used first (without obtaining the other's permission).
Even if no law is preventing you from doing so, if the action is wrong according to natural law then it would still be wrong to do on a personal basis - in the same way pickpocketing would be wrong even if there was no law enforcing it.
The argument whether or not the "natural limitations" verses no limitations makes a difference here is definitely worth considering however
Would you object to someone erasing them? If so, then the property is more than the physical medium on which it is distributed.
If I sold someone a DVD then I wouldn't object to them erasing what's on it, no.
I agree that the data on it is part of the property, but I still don't see a claim to ownership of the "mere existence of the data" - but rather the physical property (including the internal code which holds the data).
So yes, if someone took my DVD and erased it without my permission they would be damaging my property - but that's still not the same as saying a person owns "the ideas" themselves, even after having parted with the physical copy of the data.
You can't divorce an action from its moral consequences and then ask if it's wrong in a vacuum.
You can if the action doesn't meet a definition, such as that of aggression.
For example, even if the "action" or ultimate consequence of people driving cars lead to global warming causing damage to the environment, that wouldn't mean an individual's decision to drive a car was an act of aggression.
Or on the flip side if you're just using the "end results" to define what the action actually is, then wouldn't it be "less of a crime" to steal from Warren Buffet than from an average person, since stealing $1,000 from a billionaire would produce "less of a bad end result" than doing so to a person making a modest income?
Nothing about the act of clicking or watching something is wrong in the action itself, the same way nothing about holding a knife in your hand and thrusting it forward is wrong in the action itself. In both cases it becomes wrong when done in a context that produces certain end results.
In the knife scenario the end results are aggression and force used on another party.
If we didn't distinguish between the action itself and the results there would be no difference between accidental homicide and murder, for example.
So no I was talking about the action within actual context; swinging a knife in the air wouldn't be an act of aggression, however swinging it at an innocent person would.
My argument was that uploading or downloading media via the internet (which was purchased legally) isn't an act of aggression.
Anyway, if you want to know if something is stealing, start with a definition (I don't think you've advanced one yet). Here's mine: piracy is stealing because it's taking something that someone else made, without their permission, in a way that may harm them.
My definition is that if the person is less something which they actually had, then it's stealing.
However this would have to be something which they actually possessed at the time, not just "future potential profits".