It all comes down to that fact that we don't know everything. Theories are just that, theories. If a theory can't be proven, then it's still just a theory. And until it is proven, I'll continue to think of it as just a theory.
I've always been skeptical of dark matter, string theory, and other attempts to make the universe fit the current equations. And that isn't likely to change within my lifetime.
I was met Dr Kaku a couple of years ago. As a gift I gave him a copy of my book "Bebop to the Boolean Boogie"
Now I come to think about it, I did warn him that I would be "asking questions later" ... I wonder if he's read it yet?
Dr. Michio Kaku once said that you can solve these problems simply by adding dimensions. He says that eleven dimensions is what it takes to unify it all. Kaku is a co-inventor of string theory and is looking for the one equation that explains it all.
There was an amazing article in the March 2012 issue of Discover magazine about the work of Scientist Julian Barbour and Physicist David Wiltshire.
The bottom line is that if they are right, cosmologists may expect supernovas to be closer than they appear, creating the ILLUSION that the expansion of the universe is speeding up...
There are plenty of possible explanations of dark matter. In particular, astronomers keep finding /real/ dark "things" out in space, such as brown dwarfs and lonely planets. These sorts of things are very hard to see, and have very little effect on their own. But in combination they could well provide the "missing" mass that can be detected by gravitational lensing but cannot be accounted for by visible stars.
A much more "ethereal" concept is dark energy. This is not really much more than Einstein's original "fudge factor" in relativity. Does it exist, or is it just a case of the current theory (relativity) being a little inaccurate, just like Newtonian gravity before it? Even more subtly - is there actually a difference between "real" dark energy and a fudge factor in an equation?
There is so much interesting stuff coming out at the moment. Different ways of looking at space and time and gravity. There was an article a couple of months ago about this sort of thing, speculating that gravity might be affecting the red-shifts of far away galaxies and that time may "flow" differently in different parts of the universe, to the extent that -- essentially -- some parts of the universe may be "older "than others ... sort of thing...