> The results of _all_ of these experiments do not fit with the naive theory. And they each can be fit perfectly by adding in dark matter. But that's not important; the crucial point is that all of them can be _simultaneously_ fit perfectly by adding in the _same_ amount of dark matter. That's practically the definition of what a good scientific theory should do. Put in a single parameter and explain a hundred observed results.

Slightly off-topic, but can I ask if dark energy has anything like this going for it?