> "Just a thing" is a conveniently abridged version considering capitalists can only own anything physical in the first place because their government took it from someone else under threat of (or actual) physical violence
But it's not really wrong, it just ignores that the same is just as true of other economic systems, what differs is simply the model of property rights.
To address the (unfortunately dead, because while wrong it's a point of view which is common enough that its worth correcting, and not present in an inappropriate way) grandparent post:
> Given that "capitalism" is a word used by socialists to describe the absence of socialism
No, it's not. It's true that capitalism was coined and defined by socialist critics, but it doesn't refer to the mere absence of socialism. (Marx distinguished capitalism as much from the feudalism that preceded it as from the socialism he saw following it.)
> ("capitalists" think of "capitalism" as just a thing that happens when property is respected and contract law works),
The only difference between that and, say, the Marxist view is that Marx recognizes that the capitalist system of property rights is a specific view of property rights distinct from other historical and conceivable views of property, while capitalists are prone (as you just did) to confuse their model of property with the general concept of property. Feudalism (and for that matter socialism) is just as much a thing that happens when a particular system of property rights is established, enforced, and respected, and contracts consistent with that model of property are given weight.