Here are some things you may have heard from people around you if you have decided to not get married or not have children. Also, some possible responses. I am writing this from a man's point of view, but a fair number of these responses can be used by people from other genders as well.
"You don't want to get married because you fear responsibility."
Responsibility is a good thing to fear. If you're not ready for responsibility, blundering into it will not make you responsible. Better to take responsibilities you ARE ready for. Like your career or your cause.
"You're not taking marriage seriously."
I do take it seriously. That's why I am content to wait till I find someone worthy of spending the rest of my life with. I wish people would take marriage seriously and stop marrying for sex, stability, or because their parents want it.
"You are starving. Get a wife."
I can cook or I can hire a cook. Who the fuck marries for food!
"You will regret not having someone to talk to when you're old."
First, I like being by myself. Second, I have a really close circle of friends. Third, I have a social life full of like-minded people and allies. Lastly, marriage is not a retirement policy.
"There are... Heh heh... Other things only a wife can give you."
Never marry only for sex. You can get sex elsewhere. Perhaps among like-minded folks. But heck, even paying for sex is better than marrying for sex. Marrying for sex is disgusting.
"Think about your parents. Who will take care of them?"
I will. Besides, I have already mentioned it's stupid to marry simply because you need a maid.
"You need children to take care of you when you get old."
Kids are not a retirement policy. And a large part of our culture of abuse stems from this particular set of expectations - children as vessels for parents to put their expectations in.
"You will regret this when you're old."
Most people will regret something. I might regret not marrying or having kids. But some others might regret not following their dreams when they're old. Everyone will have regrets. Everyone has to choose what those regrets will be.
To end, marriage and children are just two of many things in life that you can do. It's not something you have to do. And it's definitely not a magic pill that will solve all the problems in your life. It might actually make matters worse. It often does. We need to stop being superstitious about the alleged magical powers of marriage. Marriage isn't evil. But it's not something that necessarily makes your life better. It's an option, like everything else.