Rhetoric in Ambiguity

In one of the assigned readings, the author stated how politicians' words are filled ambiguity which is a not a useful method of rhetoric. I feel that I disagree with that statement. The purpose of an argument is to convince others of what you are saying, and sometimes by not giving a definitive answer it gives room to interperate, which is sometimes more convincing. Also, making an argument for something where the complete answer is not known is avoided, by giving more of an ambiguous answer. I feel that people are always on the search for a definitive answer, and I do not know why it is very wrong in saying that you do not necessarily know what the answer is to some problems. Politicians give straight answers, but then if it does not work out the public says that politicians are liars. If politicians say that they do not know exactly and give vague answers, the politicians are not doing their job properly. People are only able to predict so much about the future and reprimanding others for not trying to predict the future properly is not what the general public should do. I agree that if you are arguing for a certain law or policy than you should give the general facts and potential consequences, but to give definite answers for every aspects of the policy is very hard to do.