Sometimes when I'm hesitating to reply to someone for whatever reason I start off with a draft response. Then if it works even as a draft, I set it to automatically send some time in the near future, enough time that I would be able to change it if I needed to. Writing things like this helps to clear your head, and if you can give it a little time, when you come back to it often you find things that could be better. Then it's just a matter of hitting the send button.