Sometimes we seem to need to use nouns with no regard of whether they are definite or indefinite. One instance is when we want to define things. Consider the following example:
On the one hand, testimony is often thought of as an intentional act on the part of the speaker and, on the other hand, testimony is often thought of as simply a source of belief or knowledge for the hearer. Source
In the text, "speaker" and "hearer" are mentioned for the first time, and no definite speaker or hearer is in writer's mind, because the sentence is defining testimony. On the other hand, to use indefinite articles would obviously be misleading too. It seems to me, therefore, that in sentences such as the above one we should not use any article with the nouns in question.
One way out of the above problem is to use the plural form of such nouns. But then in some sentences, such as the one mentioned above, to use plural forms can be misleading too.
So, what is wrong about just using no article with such nouns?