Shouldn't we as scientists be more careful with our words, and say that dark matter is BELIEVED to make up more of the universe than does visible matter, based on our current leading theories?
A very good point, and one that often is missed when talking about scientific subject.
But one also has to differentiate between what is reported that a scientist, a group of scientists, or a scientific study says, and what they actually say.
Quite often, what is reported is a complete misinterpretation of what was said, or is being intentionally made wrong in order to make a sensationalistic headline.
One other thing that is often missed or ignored by media reporting on scientific matters is that there often are different possible explanations, and that different scientists work on different studies of the same thing at the same time and might come to conflicting conclusions that are both as probable.
Scientists or science is often referred to as one coherent group with one mind. =P