Once you consider that a group might be something with a life of its own, saying that you belong to that thing sounds very much like saying that you are the property of that thing - and that is not far from the truth. A collective tends to treat its individual members very much like property. The stronger the collective, the more this is true. The strongest collectives will actually try to prevent you from leaving, and may even continue to try to reclaim their property (you) after you have escaped.

Consider cults that keep members captive, or Soviet controlled East Germany that put up walls, barbed wire, and armed guards along its borders to keep people in rather than out. Just because your religion or nation is not at that stage (yet), doesn’t make it any less the same sort of ideological animal that will tend to act as if it owns you.