Encourage the person who asked by acknowledging their curiosity or the difficulty of the question. That's a good question, you've really done your homework on the topic!
Pro Tip 2/3
Prompt Deeper Discussion
Use it to stimulate more thought and conversation on complex subjects. Good question! That opens up a broader debate about ethics.
Pro Tip 3/3
Acknowledge Rarity
Shows appreciation for a unique or rarely considered question. Wow, that's a good question. I've never really thought about it before.