In writing an argumentative essay, I have learned that it helps to pick a topic that you are passionate about. But when I am defending a position that I am passionate about, the last thing that I want to be is wrong in what I am using in evidence. If I am going to persuade the reader to what I am talking about then I have to be accurate with nearly indisputable evidence. That is why it is important to use critical thinking and evaluation in your research for your argument. .
One example of critical thinking that I would use would be looking for fallacies with rationalization. If I were making an argument over moral sense in the human race I would be careful using opinions from a writer that usually writes fiction as a supporting source. An exert from Mark Twain's book Letters From the Earth about the damned human race he has many opinions in which I agree with but he ventures off into what seems to me as fiction stories included. For example, he talks about an experiment that included many humans with different beliefs being placed in a locked cage and they eventually end up killing each other over their different beliefs. This was an extreme way to state his point but is far from "gospel". So the reader will be less likely to believe you or your argument when using sources that are fiction.
Another way to use critical thinking is to evaluate your source and use their statistics if they are accurate. As they say, numbers do not lie. In Charles Sykes book Dumbing Down Our Kids he starts off with a barrage of numbers and stats to get the reader on his side of the argument quick. A lot of these sources are credited and very accurate because he pulled them from areas like news articles. I believe since he started out this way that he logically had the reader on his side, so when he starts writing passionately afterwards it electrifies the reader even further.
A very important step to argumentative writing that requires critical thinking is having the correct response to opposing opinions and writing them in your essay before concluding.