There's an instinctive refusal to the suggestion, largely based on how blatantly he denies anyone access to his blood. Bruce does try not to be hypocritical. It's less a moral absolute for him than a general distaste toward violence, and toward betraying privacy without permission. Yet he can't deny its potential usefulness here, and if they want answers, sometimes they have to make sacrifices.

This isn't one they have to make yet. "How about we try asking them first," he answers, cautious. "We don't need to get-- drastic unless we're desperate."