When you are evaluating your material for an informative speech, you should be particularly careful to make sure the material is not
biased
ethical
specific
complex

a) Biased. Because you stop been arbitrary and take a side whether positive or negative about the object of study. Losing Objectivity and arbitrarily. And when you research in order to know about a topic you have to know the good and bad to build a strong hypothesis with enough arguments, to be capable of prepare a defence in case someone wants to false it.

Explanation:

The concept biased means that the posture is inclined to one side: positive or negative, without being objective. Thus, an informative speech has to be objectively neutral or arbitrary: which means without taking a posture to speak in favor or against the phenomenon or object of study. Objectivity is considered, to tell the truth about something including positive and negative. When your objective is to inform, you have to describe as much as you can the object or phenomenon. In contrast when you want to take a posture to support or false that phenomenon you can take a side.