Can I prevent responses from writing to the Knowledge Base?

Yes. In the Accounts page, you can modify the settings so that the default switch is always set to OFF (do not write).

Your Managers and Administrators will be able to decide what responses are written into the Knowledge Base. So they can go through the proposal after the fact and select the new items to include in the Knowledge Base. 

To modify the setting, an Administrator can go into the Accounts page and select the Settings tab.

Feedback and Knowledge Base