I'm super late to this discussion, because I haven't been on YLF for two weeks, but here's my two cents. Whenever people criticize the choices of others, it always strikes me as a demonstration of insecurity. If you are confident about, and happy with, your own choices, you don't feel compelled to criticize other people. End of story.
A couple of other points, thought. People who have children may indeed have those children for comfort and support in their old age. Ask me. I'm there for my dad through my mom's long illness. Having kids isn't a guarantee against loneliness or abandonment (who knows? Your kids might disappear halfway across the globe, and that's their right and their choice), but if you do have children, the possibility of a relationship with them exists. You can't get companionship or support from kids you don't have. When all your friends are old or dead, children and grandchildren might bring you joy. Or maybe not. *shrug* I don't have a crystal ball.
Having said that, aging parents have a responsibility to engage in social activity that doesn't directly involve their children. Their kids have their own lives and responsibilities. Parents also have a responsibility to plan for their own care, if possible. No one wants to be a burden, and no one wants to be an involuntary caregiver. (Emphasis on 'involuntary'. Lots of people gladly choose to be a caregiver to an ailing parent. But it shouldn't be compulsory).
I also know that sometimes having children seems worse than not. Nothing is more excruciating than watching a child struggle, for ANY reason, and not being able to 'fix it'. There have been times when I've wondered if I could have protected my heart by not having children.
I appreciate that choosing to be childless in India is tougher than here. Well done for holding strong. (Maybe you could plead infertility, and fake a tear or two. That tends to shut people up, lol). I think women get more flak for it than men, as if choosing a life without children is somehow aberrant. This irritates me.
Bottom line: choosing to be childless (child free, if you prefer) is fine. Choosing to have children is also fine, provided you're going to try to be a good parent and you don't have more kids than you can afford. I wish people wouldn't get their panties in a bunch about it. You are under no obligation to provide grandchildren for your mother-in-law. Tell her to volunteer at a shelter, or do something else useful that involves needy children.