I've never seen bad drawing destroy a good idea. On the other hand, I've never seen a good drawing save a bad idea.
I have no idea what readership is of written editorials, but it doesn't come anywhere close to the readership of editorial cartoons.
There is too much illustrating of the news these days. I look at many editorial cartoons and I don't know what the cartoonists are saying or how they feel about a certain issue.
It is a peculiar art form, but I think it's a necessary art form - and I do believe it's a noble art form.