This is good one to tell to people who view your writing as a hobby, or as something that will never make you money, or who diminish it in some other, unreasonable and inappropriate way (because anyone condemning any art-making is totally unreasonable and inappropriate):
Tell them: “I do the service that will improve the world.”
You don’t have to explain your choice to write, to justify it, or to reason with those people who will attempt to tell you they know better and try to drag you into an argument.
The mere fact of writing bringing a smile to your face is improving the world.
You sharing your writing with a reader—just one reader—and making that reader happy, or making that reader think, or making them ask you questions, is improving the world.
You experiencing emotions and “being in the moment” while writing is making you calm and content, and that is improving the world.
So you see, this is self-love, and self-love is the greatest service you can render in your lifetime—to yourself and to those around you.
Keep on writing. The world depends on you, as do we all.