What is the notion of something being someone's property, though, if not an entitlement? The problem with this analysis is that it's completely dependent on what entitlements you are willing to acknowledge. There is no such thing as an empirically readable tag on an object or a particular combination of bits that identifies the owner; the notion is entirely constructed and maintained by humans, and therefore the weight of any particular notion that "A owns X" depends on which and how many humans believe it.
On one end, pretty much all members of our society agree to and hone people's titles to movable objects like, say, a car. If the car is parked in place A, the owner is in place B and a random third party is in place A, then we believe that the owner has a moral right to demand that the random party not take the car, even though in some real sense the third party currently "has" the car, or at least has access to it. A hypothetical society in which people only believe in a very narrow set of property rights along the lines of "you have the right to not have your things ripped out of your hands" might write something like: "If you can't protect it or hold on to it or make sure that nobody else lays their hands on it then do without."
If you consider, say, building squatters and their supporters, or public-right-of-way advocates, this intuition that government-granted title counts is already not nearly as universal for certain pairs of property and owners; a nontrivial number of living humans appears to believe that an individual living in a building or plot of land has more of a title to it than a faceless landlord nominally owning it without putting it to use out of some abstract economic consideration. In the eyes of those who tend to side with the squatters, it is the landlords who are acting entitled to somebody else's home, just because they paid money to get an official-looking piece of paper from another unrelated entity. (This becomes more apparent in cases where there isn't a single continuous government in control of an area. If governments A and B claim a territory, person X buys a title to a plot of land from government A and person Y buys a title to the same plot of land from goverment B and then they squabble over who gets to move in, which one is "acting entitled"?)
There generally seems to be far less consensus once we talk about titles to "property" that is not even physical, and/or can be cloned rather than moved at zero cost. Is someone who designs and places a building in a public space entitled to restrict reproduction of its appearance in photos? (France says yes, most everyone else finds this ridiculous.) If we forget about reproduction, am I entitled to freely sell or give my unique copy of a book or game to somebody else, or is Valve or the author entitled to stop me from doing so? (Many Americans seem to lean towards siding with the publisher, a parallel thread mentions that the EU just reaffirmed that the publisher's rights are exhausted with the first sale.)
Other cases where people disagree about whose title is valid : taxes, patents, copyright duration...
You need to recognise that many anti-copyright campaigners come from a moral framework where the creator of a book or movie has no meaningful title to what someone does with data that they have stored; in this framework, it is the copyright owner who is by default assumed to be acting entitled to someone's manifest property (a sequence of bits on their harddrive, which they are not withholding from anyone else). Often, this goes hand in hand with a basic moral intuition that ownership := you are entitled to not lose use of the thing := you are entitled to not have others gain use of the thing. (That's why "you wouldn't download a car" is so universally made fun of in anti-copyright circles. It makes sense if you think of the point of owning a car being that others don't get to use it.) You might persuasively argue that this notion of property/pattern of recognised titles is inferior to yours - and this is the type of argument that is being made whenever people debate whether patents encourage or stifle innovation, rather than making the debate about whether the inventor or the commons is acting entitled - but to simply assert that the studios' title is valid and the copy-holder's title is not is as useful as shouting "no, MY moral principles are right".