An opinion can feel personal because admitting where you borrowed it would feel impersonal.

Opinions arrive from somewhere and then get naturalised. The view came from a book, a friend, an article, and admitting that feels like conceding that you have not thought about it, so it quietly becomes yours. The defensiveness is about wanting the position to be evidence of a mind rather than evidence of an influence.

Try saying where an opinion came from next time you offer it. It costs almost nothing and it makes the conversation better, because the source can be examined. It also loosens the grip of positions you have been holding mainly because they became attached to your name.