The best response to someone saying, "I don't want to be friends with benefits" would be to acknowledge their feelings and communicate openly about your own expectations and boundaries. It's essential to be respectful and understanding, as this can be a sensitive topic for some people. Here's a suitable response:
"I appreciate your honesty and understand where you're coming from. It's important to be on the same page when it comes to our relationship. If being friends without any physical involvement is what you're comfortable with, I completely respect that. Let's talk about what kind of friendship we both want and establish clear boundaries to ensure we're both happy and comfortable moving forward."
This response shows that you value their feelings and opinions while also initiating a conversation about defining the nature of your relationship, ensuring that both of you are on the same page moving forward.