The problem here is that d_i_r_t_y wants to have two parallel conversations within one browser, and you can't do that purely with cookies, because the browser will happily send the identically same cookie to both "session" hits.

Well, there are ways around that, if you really, really wanted too, but you'd have to have the server do more work than it should.

I am definitely in the "both" camp, however: allow for a user to use cookies or not use cookies, as they please. Not that I'd ever use Amazon as an example. :)