Isn't this behaviour exactly the same as with commas at the end? Here, to comment out the first line you would need to edit the second. With commas at the end, to comment out the last line you would need to edit the second last. Other than that, no editing of other lines is required.
In fact, in a language like Javascript where extra trailing commas are allowed, it seems that this argument makes even more sense for commas at the end than it does for commas at the beginning. Then, there would never be a situation where you would have to edit a line besides the one you were commenting out.
Trailing comma in SQL is a syntax error. It's also not allowed in JSON. And editing second last line can be a pain if you're testing something and are commenting/uncommenting the last line repeatedly.
Not if the line you're commenting out is the last item of a select or a join command or an AND within a where clause. Sorry Gould have made better example
But it was 4 am :)
In fact, in a language like Javascript where extra trailing commas are allowed, it seems that this argument makes even more sense for commas at the end than it does for commas at the beginning. Then, there would never be a situation where you would have to edit a line besides the one you were commenting out.