I don't disagree with you. I'm not siding with Google or Fastmail and I don't use their services but I can see why would someone leave Google and choose Fastmail just because they don't want to be tracked by Google. Of course that's not to say their email is safer than it was with Google because the vast majority of people use Gmail anyway and your plaintext emails find their way to Google's servers one way or another. NSL's are also a factor, but that depends on your threat model. Not a lot of people will be bothered by the threat of government agents seeing their emails by getting an NSL, so eliminating the company tracking will be enough for them to feel secure. Which is, of course, a false sense of security and is bad.

We know the NSA was planting code and hardware and employees at will into our country's top infrastructure. It's highly unlikely PRISM was the only program which would get user data out of Google without their permission.

If you prove one of my servers is infected I'd be wrong to assume it's only got one backdoor.