Which idea, exactly? Dark Matter is not a theory. It's the name given to the observation that things at large scale don't act in accordance with how general relativity says they should. Multiple theories have come up to attempt to explain this, broadly in two categories: new particles and changing the gravity formula. But scientists really don't have a clear idea of what the right answer is.

As someone doing my PhD on this topic, there aren't even any theories really competing with dark matter, and dark matter fits what we see in the universe quite well.

That being said, we're still quite in the dark on what dark matter is, but we're pretty sure its there.

... the double slit experiment [makes] me angry.

I think if the conclusion of the double slit experiment doesn't make you a little upset, you're not really paying attention to the implications.

I think Wheeler's delayed-choice experiment, with all its variations, shows a particular obsession with trying to get a definite answer from the universe.

The fact that it is possible to decide whether a wave or particle feature manifests itself long after—and even space-like separated from—the measurement teaches us that we should not have any naive realistic picture for interpreting quantum phenomena. Any explanation of what goes on in a specific individual observation of one photon has to take into account the whole experimental apparatus of the complete quantum state consisting of both photons, and it can only make sense after all information concerning complementary variables has been recorded. Our results demonstrate that the viewpoint that the system photon behaves either definitely as a wave or definitely as a particle would require faster-than-light communication. Because this would be in strong tension with the special theory of relativity, we believe that such a viewpoint should be given up entirely.

The universe we inhabit is a goofy, nonsensical place that frustrates our attempts to comprehend it.

The evidence for an undiscovered particle (or family of particles) as an explanation for the gravitational oddities we see throughout the universe is pretty overwhelming — certainly compared with the evidence for competing theories.

I think the big failure in "selling" the lay public on dark matter has been a failure in explaining exactly why dark matter particles are so hard to detect and classify individually despite being so obvious at cosmic scales.