I have a male colleague who is very upset when his wife is asked this questions by her ( female)colleagues and has also been asked the same question himself. Having said that my immediate colleagues will insult each other until the cows come home, but would never dream of being rude enough to ask anything like that. After all half the department are, for three totally different reasons grieving children who never were, but who would have been much loved if they had been. My husband and a similarly childless good friend who is male have had a certain amount of grief from men who are fathers about their childless state. All the men I know who have had this hassle say that they think women get this worse.
There are a very limit set on conditions when it is my business to educate someone on fertility. When DN, aged 5 asked me when she would be having a cousin and could she cuddle the baby if she was very good and sat on of the sofa sensibly, that was fine, we had a bit of a talk about how babies grown in the different bit of your tummy to where the food goes, and sometimes that bit doesn't work so well especially when women get older. I also mentioned that some people are sad about this, so although it's Ok to ask me or Mummy or Daddy or Granny anything, maybe it's best not to ask other people.
It's not so much the questions that hurt me or have hurt me in the past, it's the other remarks. "Not being a real woman" "not knowing what love is" "It doesn't matter is you die because you aren't a mother" "You must hate children" "You don't know what unconditional love is - you can only feel unconditional love when you have given birth (um - isn't that a condition, and very, very nasty to adopted and fostered parents and children.) I did a fairly big favour for a new colleague once and was told "oh, you are so kind, I can tell you have children". I couldn't carry on getting credit for a "virtue" I don't possess, so I just said "no, actually , I'm childless." There was the indrawn breath and the "well" in a tutting tone of voice and the heel turn and door slamming. She was very clearly angry at my response. Had I known for what a short length of time she would continue to be a colleague I might have kept my mouth shut, but to have left it and had her later find out I had no child could have been awkward.
But to answer your question, yes, I normally think it's rude and often hurtful and suspect from the other things said that the intend is to be rude and to hurt on many, but not all occasions. The reason I joined here was really to try to understand what it is like from the other point of view - to find out why the people who hurt other's like this want to do that, what they get out of doing that and to try to stop myself from being hurt (or to find a way to make myself grateful that I can make them feel better by being the recipient of the bullying).