I think "lacking in insight" is an opinion, rather than a label. One might lack insight about a particular problem but not be lacking in insight overall. It's relatively easy when things feel personal to take a position that is protective of ourselves but might be wholly off base; I think we all know people who say or do something that makes no sense to us but, obviously, does to them.

I don't worry too much about a doctor's dx other than to learn as much as I can about it. If I disagree with it I find scientific evidence of what I believe it to be and point that out next time in the conversation. It's a discussion, not a hard and fast, "you're 61 years old, five feet five inches tall, brown hair and eyed, and your appendix burst May 9th 2003"; especially when it is about psychiatric matters.