Someone strongly committed to a fuzzy idea of freedom might object to private property as an institution that keeps people from achieving their objectives. It is useful to understand this point, because a libertarian's ability to persuade a socialist on the virtue of property may hinge on it. The socialist goes wrong the moment he thinks about freedom and property out of context or in an inappropriate context, cut off from more fundamental ideas. Ruminations on a concept that are uninformed by the context in which that concept exists are bound to be erroneous. If this is meant as a general proposition, it is absurd.
Theft implies the legitimacy of property.
It is the illegitimate taking of someone's property. The idea of property, like that of theft, also exists in a context. If we get that context wrong or ignore it, we have problems. Socialists illustrate this when they argue that property violates freedom and rights. Yet libertarians see it as critical to freedom and rights.