You're not "wrong" per se as you're entitled to your views, but a fairly common alternative view goes something like this.

Yes, while we sometimes do pursue scientific inquiry for its practical application to the betterment of humanity, we also recognize the value of scientific inquiry simply for expanding the endowment of human knowledge about the world. That is an "innate good". Moreover, if history is any guide, it's sometimes or even often difficult to predict what practical applications will or won't emerge from any given scientific endeavor. In the case of Dark Matter, it may not be exactly the case that we will ever directly manipulate it in any scientific application. However, it may be the case that by grappling with Dark Matter we will refine and deepen our understanding of the fundamental laws of nature, and that will unlock future practical applications. Then there is the topic of "human capital": training people to be scientists trains cadres of people with strong skills in science, math, engineering, and computer science, which is an investment in that human capital. Often, they're well-equipped to go on to fruitful careers outside of their initial field of inquiry, producing innovations that benefit humanity. Finally, if it's a matter of cost, many people feel that the societal cost (e.g. federal expenditures on science) are puny compared to other things which I need not name here. Consequently, "basic science" which includes fundamental physics and the study of Dark Matter, is always a great investment for society.

Or something like that...that's my understanding of how that argument goes. Make of it what you will.