We scientists have no idea what dark matter is. Just because this 'known unknown' accounts for most of the universe, this does not in anyway hinder our academic right to proclaim what is and what isn't.
In fact even if we didn't know anything at all about the universe and what it is made up of, our papers allow us to dismiss anything that we don't understand or know about.
It is not really about what is known and unknown. The fact of the matter is that if we can't experiment on something, because we don't know what it is, we are within our professorial rights to deny that it exists.
It is very simple: Until it is tested, understood and documented it simply doesn't exist!
Director of the Amstrad Scientific Research Centre