What is the reasoning behind the lack of conversions when passing parameters

[Walter Bright]

C++ has this, implicit conversion of structs. It looks great with simple cases. 
However, as overloading gets more complex, it becomes a source of mass 
confusion. I've had many C++ programmers tell me that nobody actually knows how 
C++ overloading works - they just try random things until they get the result 
they want. There was a lot of talk in the 90s about implicit conversion being a 
mistake, but by then it was too late and C++ has had to learn to live with it.

It's in that class of features that inevitably lead to incomprehensible code.

I tried to make overloading in D much simpler, but it's still overly complex.

Let's not dig that cat out of the pet semetary.