The EU cookie law faff from earlier this year shows that's probably not what would happen. Various people tested opt-ins for cookies. It didn't go too well. In

The EU cookie law faff from earlier this year shows that's probably not what would happen. Various people tested opt-ins for cookies. It didn't go too well. Instead, any site running a system like that, except those for which there genuinely is no alternative whatsoever, would see their visitor numbers plummet.