This technique is also called "black-and-white thinking" because only two choices are given. You are either for something or against it; there is no middle ground or shades of gray. It is used to polarize issues, and negates all attempts to find a common ground.
Either/Or is an example of black and white or dichotomous thinking. A complex problem is simplified so that only two options are presented. They are stated in such a way as to make you believe that there are no other options.
For example: "Some beach balls are yellow. Some beach balls are red. Therefore, if you have a beach ball it must be either yellow or red."
BLACK-AND-WHITE FALLACY
The propagandist technique of presenting only two choices, with the product or idea being propagated as the better choice. For example: "You're either with us, or against us."