Dusting and cleaning does not defeat the purpose. You’re making the mistake of thinking that cleanliness is boolean… true or false. It’s not that it’ll just get dusty again, it’s that it will get more dusty, and then even more dusty, and then dustier still, and there is actually no real practical limit to how filthy a place can get. Cleaning resets the progress to a point where you can live again.

Now, there is a related cleaning story that could be called defeating the purpose that stuck in my mind. It’s a bit Luddite in nature, but does have a point. It’s a micro-story from inside the book “Mrs Frisby and the Rats of Nimh”:

The story was about a woman in a small town who bought a vacuum cleaner. Her name was Mrs. Jones, and up until then she, like all of her neighbors, had kept her house spotlessly clean by using a broom and a mop.

But the vacuum cleaner did it faster and better, and soon Mrs. Jones was the envy of all the other housewives in town—so they bought vacuum cleaners, too.

The vacuum cleaner business was so brisk, in fact, that the company that made them opened a branch factory in the town. The factory used a lot of electricity, of course, and so did the women with their vacuum cleaners, so the local electric power company had to put up a big new plant to keep them all running.

In its furnaces the power plant burned coal, and out of its chimneys black smoke poured day and night, blanketing the town with soot and making all the floors dirtier than ever.

Still, by working twice as hard and twice as long, the women of the town were able to keep their floors almost as clean as they had been before Mrs. Jones every bought a vacuum cleaner in the first place.

That’s an example of defeating the purpose, where the thing you do actually makes it worse. A similar “defeating the purpose” is when a bunch of companies lowers wages to save money, making it so that people can no longer afford their products, meaning that they earn less money after all.