What if a parent comes to visit you, after you have discussed diversity in your class room? Look at this as positive, it means that the parent is involved in their child’s life and education! Nonetheless, when this happens, it is best to have a private conversation with the parent. Acknowledge their feelings and ask what the specific issue is that is bothering the parent? For all you know, there might be a misunderstanding, and you can solve this immediately.
If there is no misunderstanding, you can explain why you discussed the topic in your class. You can say for example that you want your students to learn about different topics.
At the end of the conversation, you don’t have to agree with each other. It is important however, that there is mutual understanding.
And keep in mind, you don’t have apologize for something you didn’t do wrong!