I think this topic is similar to the post about a newspaper charging for comments.
Publishing is in crisis. I know many web types don't really worry too much about these inky-fingered paper dinosaurs, but it worries me. For whatever reasons, the web gurus of the late 90s told everyone to win eyeballs, and now we have free content, free comments and free submissions. Not even the price of postage is a barrier any more. We seem to be suffering now from an internet that is burdened by too many contributors, too much information, too much noise and not enough signal. And what the publishers will tell you, too few readers.
So perhaps a paywall will help to balance this out. In the past submitting a letter or an article or a book to a publisher was the "entry barrier" to participation. Now it is easier to do via a website or email and the price disguised within the ISP fee.
And if publishers do not charge for submission, how else do we reduce the overwhelming deluge of poor quality submissions?