Aw come on now, they do perform a service that's of nonzero value - they (ostensibly) sift the wheat from the chafe. I don't have the expertise to know what's valid research and what's hokum, but I know if I read it in Nature, I can at least take it seriously.
Admittedly I believe we could develop a much better system for doing this then academic publishing, but I don't honestly know what such a system would look like.
Uh, you do know that the editing and reviewing are normally done for these journals by mostly government supported academics who don't charge for their time don't you? The academic journal business has devolved into tax payer dollar farming with the usual campaign $$$ payoffs to establish and maintain monopolies.
Admittedly I believe we could develop a much better system for doing this then academic publishing, but I don't honestly know what such a system would look like.