Negotiations are profoundly affected by the factors you raised. Everyone has 'hot buttons' that can lead them to focus on emotional issues rather than the subject matter of a given negotiation. More than twenty-five years ago, a relative of mine was negotiating to buy some property from a womens' organization, the YWCA, for a commercial real estate project. All hell broke loose. The business deal fell apart as a result of my relative having activated the 'hot button' of another party.
Negotiation is the process by which human beings exchange items of value in a civilized manner.
In response to your question, 'human beings' is the important phrase. People make assumptions about themselves and about the people with whom they are to negotiate. If we put people in pigeonholes, if we assume that everyone from a particular ethnic group, sex, company or whatever is going to respond in a predictable way, we are not treating them as individuals, but rather as objects. In negotiation we may well walk into the process with assumptions, but we have to test whether those assumptions are valid in each case. We need to ask questions and listen for answers to find out whether our assumptions are valid.