I spent a couple of hours looking for a set of good instructions, that explain how to turn off comments globally in WordPress without altering the code. None were very clear but most referred back to the bulk edit setting.
Here are the references in the codex:
It was very confusing when I could not see the bulk edit options talked about when looking at the post screen. I was missing something in the translation. Then the light went on : I had to do something to get at the tools they were mentioning.
Just check the box next to all Post / Pages you want to apply changes to and choose the Edit and Apply from the drop-down. The view will change to give you options in the bulk editor. Choose: Do not allow, and all comments are turned off.
You may set Pages and Post comments to allow or disallow, on an individual basis in the edit page or post . Check or UN-check , Allow comments in the lower half of the edit panel under discussion .
So don’t edit your themes code! Settings for comments in general are in Settings / Discussion. But if you really just want to turn them all off entirely you can do it with the bulk edit setting .