Why is calling her "Thai Lady" disrespectful?

Context:

Incident: During surgical rotation, a group of students on rounds visited a patient who was from Thailand. Her English was broken, but she clearly could understand most of what was said. The resident walked into the room and announced, "OK, here we have Mrs. Thai Lady."
Response: This case is so valuable to discuss because it is an example of lack of respect for a patient. One of the principles of humanism is that we all owe each other respect. This case is particularly painful to contemplate because it involves a person who is perceived as not fully fluent in English and is easily stereotyped into an ethnic class. The comment also betrays a certain lack of appreciation of her humanity, reducing her to "Thai Lady." She is a patient, and although this kind of comment would be abhorrent if it were used referring to a colleague, it is even more so because patients are our very raison d'être.
Perhaps the resident thought that this was a humorous introduction to the patient as he grandstanded on rounds, seeking peer approval. Yet the comment is alienating for the patient and, therefore, has no place in a therapeutic relationship. I hope that the resident may come to recognize that reducing a person's status in no way endears him to members of this caring community.

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In addition, what does " our very raison d'être. " mean?

Is it French, meaning "goal or reason of existence"?