Actually no that’s not what it said. Or at least not in the way that your terse paraphrased summary suggests.
What it actually does is list a number of reasons why distro themes are bad (in their opinion). Some of those reasons amarettos equally true for end users theming and some of those reasons are not. The letter also does say that end users are welcome to theme themselves but they should do so under the knowledge that there be (potential) dragons.
What it doesn’t say is that theming “doesn’t work”
Personally speaking, I’m on the fence about whether I agree that distro theming is bad. However I do think their points are perfectly valid and that a considerable number of HN commentators have taken the letter completely out of context.
Edit: and I’m also a little peeved that there is so much knee jerk down voting of comments on here. Particularly when those comments are quite literally correct. It’s a really pity you guys couldn’t be bothered to read the letter before abusing your right to moderate.