Chiefly and most basically, among all things, people want to "own" the prosperity of their personal labor and risks. It is one of the most intuitive and universally accepted ideas among our species.
People sign contracts and make agreements, but then there's always some guy with a chart trying to tell them these were invalid with one corner of his mouth, that they got screwed and should have owned more with the middle of his mouth, and then somehow that "property is theft" with the other corner of his mouth.
I have no issues with collectives, or the sometimes virtuous notion of collective property, but I do take issue with them being forged involuntarily with other people's money.