While I haven't voted on that question at all, I think the biggest problem with it is that it really isn't a parenting question. Now before I get downvoted to oblivion, let me explain.
As I read it, the OP went to a doctor's office, overheard a nurse say something she didn't like, tried to address it and didn't get a satisfactory response. Then the OP asks "What should I do?". Well, that question doesn't really have a parenting angle to it. It's very open ended and, given the context, leans more towards an interpretation of "how do I deal with this nurse / doctor's office?" That's a pretty general question and not really parenting specific. The fact that this took place at a pediatrician's office seems very tangential to the question being presented. Replace "pediatrician's office" and "comments about spanking" in the original post with "any other doctor's office" and "comments about something offensive (possibly racist, sexist, medical practices you disagree with, etc.)" and the problem, answers and the question presented really don't change that much.
Now if the question had more to do with the OP's daughter, it would likely be a better fit. For example, if the question presented was
I took my daughter to her doctor's office the other day. A nurse
there made a comment to another parent that he should discipline his
child by spanking. I was very upset by this and have decided to do
{X}. How do I explain to my daughter why I was so upset?
Or
I took these steps to try and address the situation, but it didn't
work out the way I wanted. This isn't going to stop me from fighting
for the things I believe in. However, I am having a hard time
explaining to my daughter how not to get discouraged when things like
this happen. How can I better explain to her the need to always stand
up for what you believe in?
Or
When all this happened, it really upset my daughter. How can I help
her get over this?
Or ...
This or any number of variants involving the daughter here would be a far better fit for the site. As it stands, it is really more of a general life question that happens to involve a child.