Ha, what if the 'rule' is 5 lines long?
Many times, a Makefile snippet in an HTML page or a PDF file has had the tab character auto-magically morphed into spaces. So when it is copied, it will be a syntax error in a Makefile. Even copying Makefile snippets from one terminal window to another will eat those tab characters. Fortunately my vim editor is configured to handle most of those edge cases now, but it took me... I don't know... 10-15 years to get that right.
My personal rule is that control characters which are visually indistinguishable from other characters have no place in source code which are meant to be written, read, and copied by human beings. So yeah, that includes the <tab> character. And yes, I do think the Golang people got that wrong, although the 'go fmt' command largely solves that problem. Except when reading Go source code on web sites which don't handle tabs well, and you are nested 6 levels deep, and half the code is unreadable because it's bled off the right side of the page.