Here's a draft - let me know if there's anything in here that comes across as too judgemental, or might otherwise cause further damage:
Dear W,
I have given this a lot of thought, and I do appologize for not responding to you sooner. I am not going to be taking the time off on the 3 days you asked me to. There are two reasons for this: 1. it is going to be crunch time at work as I have a deadline of 8/15 for a very important project 2. the message implicit in my taking this time off is that I agree with what you are doing, and I am in fact making it much easier for you to do this. This message goes against my values, and therefore, even though it is sure to make you angry, I need to do right by my self.
I hope you understand where I am coming from. I am not trying to prevent you from doing what you want to do, but I do not want to be part of it.
“No problem can be solved from the same level of consciousness that created it. ” – Albert Einstein