html/template is literally nothing more than an "HTML-safe" version of text/template, which is Go's arbitrary text template language. It's meant to be completely a drop-in replacement for text/template, and as such, its design does not give HTML output any special consideration, which an HTML-specific template language would.

I understand the point you're making - I just want to point out that Haml is explicitly designed for HTML, whereas html/template more or less "just happens" to be useful for HTML.

As for ERB, I'm not convinced that it is too different in this regard. I'm not much of a Rubyist, and I find it incredibly frustrating to use, but perhaps that's a matter of personal preference.

{text,html}/template have their warts - I literally started Jetpack because of an unusual html/template quirk I ran into that was tricky to debug. However, I don't think it's any worse than other template language in this regard (my main points of reference are Jinja2, ERB, Haml, and Scribble).