Beyond that, the complexity of a language has nothing to do with how much you need a debugger. If you are writing a complex program, you sometimes need a debugger to quickly figure out what is going wrong, instead of endless theory -> change/log -> rerun cycles.
I disagree. There is a higher chance you need a debugger when trying to understand, say, Scala code versus Go.
> If you are writing a complex program [...]
Complexity of a program depends on its author. Even a stupid simple function can get complex if the programmer is less experienced. Go has a philosophy to simplify things. The community tries to follow this philosophy as much as possible, which is why a lot of Go code is easy to read regardless of how complex the logic is.
In the majority of cases, a need for Go debugger means you are dealing with bad written code. Heck, this idea can be extended to pretty much any language.
Simple code often doesn't need a debugger to be understood. Complex code sometimes does. But code can be complex simply because the problem domain is complex.
Also, a simple tool can very well introduce accidental complexity than a more flexible (and therefore complex) tool. Go is famous for doing so with many of its design choices.
A very good example is if you want to perform a set union of two collections. In many languages, you could simply create a set from each collection and then run the union operation on them. In Go, the easiest way to achieve the same is to use maps and rely on the fact that the keys of a map happen to form a set, while ignoring the value part of the map entirely. This is not only inelegant, it is also unintuitive and it wastes memory, but is at least slightly less complex than writing a set data type for your struct by hand.