But parameters don't just fall into FooBar shaped holes. Someone passes them in there. Its still an explicit choice by the programmer to not read the docs and just roll the dice. Who thinks "I fits, I sits" is sufficient for a proper program anyway? Is it really a downside to allow this kind of munging?

Personally I want to see Extension Interfaces, so you opt into such a system in a slightly more explicit way. The slightly extra work aides in tooling and documentation but I can see how Go's way is not absurd.