I don't even understand the 'have to learn a debugger' statement. Is he referring to things like pry? I rather enjoy the debugger in Rubymine, and part of the reason for this is that it more or less works like every other debugger I have ever used (eclipse, vs, chrome debugger, etc.) There is not much to learn if you have used any debugger in the past.
GDB is not innate.
Therefore GDB has to be learnt.
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I don't understand your lack of understanding :)
EDIT:
Addendum: Symbolic debuggers like GDB are non-trivial to pick up, is that what you're arguing against?