- If it was done to them, they don't want to think of themselves as damaged.
- If it was chosen by their parents, they may want to defend their parent's decision. Plenty of people rightfully want to protect their parents.
- Some desire to protect the routine as a part of their religion. Challenging any part of one's religion can be very scary. People don't want to be an outcast among their religious group.
- Some don't want to believe they made the wrong choice for their own child.
- Some want to believe that their doctor and/or medical system has told them the truth.
- Some are medical professionals that can't even consider the possibility that they have been performing a procedure (or supporting a procedure) that hurts people.
This may be redundant, but this helps explain: https://en.wikipedia.org/wiki/Cognitive_dissonance
As an intactivist, I keep this stuff in mind and not take it personally.
