His social identity will play a either a small role or a large role based on what he is presenting. For example, if he is presenting on how to grow a plant his social identity will play a small role because he cannot influence anything that has to do with growing plants. Your questions are based on opinion so I will answer based on what I would think. I would not believe him more just because of his color or race, if he had experience in growing plants I would believe him more based on this information, while if they had never grown plants I would be less likely to believe them. I would not have a different opinion if they were a person of color. I think that he has experienced discrimination before simply because everyone has. The level of discrimination that he has faced depends on his backround.
