I didn't get a whole lot of negativity from people (probably because I'm a scientist and they assume I know more than they do, so they don't want to question me!), but when people did question it, I always said I was choosing to birth at home because it seemed safer and easier and less painful than birthing in a hospital. In fact, it turned out that it was. I had a really positive birth experience, didn't ever feel like it was truly "painful" and I felt very relaxed and in control. I also had a 4 hour 2nd (pushing) stage, which isn't unusual or anything to necessary be concerned about (baby and I were both fine, she was posterior and turned before birth which is why it took so long), but had I been in hospital, they most certainly would have intervened using forceps or ventouse, which would have caused more trauma for me and potentially injury to my daughter. I have some friends who had forceps births and their babies had awful facial injuries. So it most certainly was safer.
But I agree with the PP, if you are choosing a home birth (or whatever kind of birth you're choosing), you should be choosing it because it's where you feel the safest and most comfortable. If I had at any point felt like I would be safer and more comfortable in hospital, I would have birthed there. I birthed at home because it seemed safest and best to me and I felt really confident that my midwives had the tools and skills to handle any situation that arose. I think you really have to buy into that and believe it yourself if you want to have a positive experience (in any birth environment, not just at home), but also to convince other people that it's the right choice for you. For me, it was never a scary choice, so it was easy to communicate those feelings when I talked to anyone about it.
That said, I don't think it's your job to convince anyone of your birth choices. If you were having a c-section, you shouldn't have to convince anyone that it's an acceptable choice, and home birth is no different. If they aren't the ones giving birth to that baby, they don't get to voice an opinion about it. If you don't feel comfortable talking about it, just say it's not up for debate and it's your choice and change the subject.