The OP's argument doesn't hinge on "I'm offended." They give several reasons why Atwood argues from ignorance. Comparing suicide with ragequitting is a horrifically callous thing to do.
Many other people have managed to express Atwood's point before his mostly superfluous post (e.g., Lessig) in a much more appropriate manner.
Those who are dead don't mind. (One of the things forfeited in death is the right to be offended.)
Atwood's interpretation and, essentially, anger and disappointment is one of the ways that survivors try to come to terms with suicide.
That it might not be a clinically correct interpretation, in any one particular case or even most cases, may not matter. Does it help Atwood? Might this framing help others get on with their lives?
If you think this 'ragequit' analogy will harm the living at risk of suicide, do you have evidence for that view? I think its effect could go either way: such judgmentalism is unlikely to reach the severely suicidally depressed, but might interfere a little with some mild/early suicidal ideations.
I'd like to summarize by saying that criticizing someone else's way of grieving as 'inappropriate' is itself inappropriate. I'd like to say that, but I can't, because that'd be more than a little self-negating. Whipping out our various still-vital impulses for indignation and criticism is another way that we, the living, poke each other forward.
It's callous because it displays a severe lack of empathy and understanding. As someone who has suffered from serious depression and suicidal thought (to the point where I physically harmed myself) I can say that I was disgusted by the notion of suicide being a deliberate, egotistical choice. I'm disappointed in Atwood, and I can't help but think less of him now.
You're hallucinating most of what you take to be my opinion, to the point that I wonder if it's a waste of time trying to correct it. (I.e., assuming that I consider the dead to be offended by Atwood's post, that I think it harms the living, etc.)
Being callous means showing a lack of empathy toward others, in this case people who are depressed. Not all depressed people are dead.
Atwood's post may very well be self-therapy, but that doesn't immunize him from the social fallout of his post. One could might argue, for instance, that Achilles' effort in the Trojan war was his way of coping with the death of Patroclus, but that hardly condones his war crimes.
Many other people have managed to express Atwood's point before his mostly superfluous post (e.g., Lessig) in a much more appropriate manner.