Earlier quoted context omitted.
That may be, but people are not property. Or, well.. should not be.
You do realize that the system of property doesn't apply to actual objects? My house doesn't become green if I write so in the deed. The system of property is a set of obligations imposed on people , not things. Much like the social contract.
Another difference is that the "system of property" actually works to everyone's favour - quite the opposite of "the social contract", and imposes no other obligations on you than to not aggress against anyone else's property. If "aggress" sounds out of place, let's say "interfere with someone's (exclusive) control of their property". There's lots of room for pointless bickering in moral issues, etc.
There are various sensible ways to view the concept of property. One is Murray Rothbard's idea of something becoming your property by "mixing your labour" with it. For example, if you build a house, or plow a corn field, they're your property.