Even if you agree with the increase, say no, you don't agree with the price increase. My reason why, is the same reason you could use in about every other situation.
Microsoft Price Increase - the response from the public was positive about it and didn't mind the increase. Then you know what that means? That means, MS would know it wasn't much of a problem increasing the price of XBL Gold. And would much more likely increase it again.
If the public instead is upset and negative about it, MS would less likely raise the price of XBl Gold again.
If you don't mind the raise, then you are encouraging MS to do an increase again, its very simple.
Just say no