I think he's absolutely right that writing is no harder than anything else--it's just hard in different ways. Or to use my favorite quote about writing (from Red Smith): "Writing is easy. You just sit down at a typewriter and open a vein." (I got that one from Denny Lien, as I remember; he agreed with it, and so do I.)

And I think Garrison has a right to be tired of writers whining--if he applies it to every kind of work. That is, if he thinks no one should complain about their work, well, that's his preference and it's his right to say so. I tend to agree with him that some artists--not only writers--do tend to "self-involved moaning over the agonies of" their work in a way that, for example, police officers and emergency room doctors do not.