I think I have to disagree with this one.

A major part of being an effective programmer is the ability to maintain state and call stacks in your head.

Stepping through code is great - as a last resort. But I've found that if I need to run through it with a debugger in order to understand it, it is often overly complex.

As with any generalized rule there are exceptions, but I consider needing to step through code in a debugger to understand its behavior as that exception, not the inverse.

Yes the diffs often don't show enough context and the errors may occur outside of the diff so you should really review the whole changed function even if you don't need the debugger.

They are always attached to a branch though so you can check it out to review (and run/test as appropriate).