Few decisions you'll make in life are as personal as where you want to labor and give birth to your baby. With nearly everyone doing so in the hospital, many people are surprised when someone says they want to have a baby outside of a hospital. It sounds dangerous and like a very... "hippy" thing to do. The first time I heard of someone having a homebirth (before I realized all my family was born at home!), I couldn't believe it. I sincerely thought she was crazy. They were from South Africa though, not America... I'm embarrassed to admit that those really were my thoughts. Surely Americans don't willingly give birth at home -- without an epidural!
The American perception of birth mostly comes from our media. Birth happens fast and is often dangerous. Either the mom or the baby (sometimes both) are in imminent danger. It's a weird phenomenon in American media, but I guess it makes for more emotional and exciting entertainment. Labor comes on suddenly, painfully, and she must get to the hospital immediately. Once her water breaks, the baby is going to fall out! Approach it from the flip side. People hear of a 30 hour labor, but all they really know about birth is what is mentioned before (sudden, painful, continuous, and dangerous), so if a labor is long, something must be wrong. And the perception is that it's fast, painful, continuous, and dangerous for the entire 30 hours. People truly don't understand birth -- physically or otherwise.
So when a couple does their research and announces that they would like to give birth out-of-hospital, they are often greeted with shock and grave concern by their family and friends.
Both my parents were born at home, and their parents, and their parents, etc. Homebirth was not uncommon for either of my parents' families. My brother, sister, and I were all born at the hospital in traditional American form with lots of interventions and drugs. David and I had our first two babies at hospitals, but decided at 33 weeks to have our 3rd baby at home. My best friend had had a homebirth about 8 months earlier and my parents knew I wanted to do the same. I didn't tell my dad about our decision because I knew he'd think I was irresponsible and stupid for choosing homebirth. I wanted my mom there to help with the other kids and whatever needed to be done, so I swore her to secrecy.
Understand that your family and friends love you and their fear comes from a place of love. They don't understand birth and haven't researched like you have. Many couples feel that they need to sway their parents or make them understand. For many people, their beliefs about birth are so ingrained.
In this woman's case, if you've been told you come across as insensitive, it's probably best to avoid the subject with those that are negative or fearful. It's sad because you likely want to share your excitement, but they probably feel that you should acknowledge their fear and opinions. It is their baby too -- or at least that is their perception.
I know of a couple that was doing online Birth Boot Camp classes and planning a homebirth. The parents -- specifically the mother -- of the father were not happy at all that the mother-to-be wanted a homebirth. She felt that since it was her grandchild she had a right to express her opinions. As you can imagine, it caused some heated discussions between the couple with the dad-to-be caught right smack in the middle. Fortunately they had some people in their lives that were supportive who were able to give information to the opinionated parents and really help them see that it wasn't their place to decide where this mom should give birth. (She had a wonderful uneventful homebirth by the way.)