My understanding of this is the following: having implicit casts between certain fundamental types has always been a source of error that even led to own classes of security issues. Instead, Go, like with other things, is going the explicit way: instead of documenting a list of implicit conversion rules somewhere, the language forces the programmer to think about the conversion, and to explicitly state the intention in the form of an explicit conversion between two data types.

And to be honest, I like code that is explicit in what it does. That makes things easier to read and comprehend.