The argument specified in the docs is "a language needs only one conditional flow construct" (in a language, of course, that has half a dozen conditional flow constructs ...)
The more palatable argument that people who try to cover for ... seems to be that when people nest if expressions, it becomes a mess. I'm glad these people exist.
The real reason is found here: http://dtrace.org/blogs/wesolows/2014/12/29/golang-is-trash/
(or if you prefer, in the compiler's source itself. It doesn't take a compiler expert to realize it's not very clean code. Even violates the go style, and the C one before that was just horrendous)
The TLDR is that Go's compiler is a "fisher-price my first compiler" and really shows that the authors simply barely knew how to get a compiler working in the first place. That they were not ready to go into a rational discussion on programming language and type theory ... is not something anyone should be surprised about.
That they avoid the arguments by dismissing the people making them in such a condescending way is ... well, there's not really anything good to say about that.
