Should advertisers have to pay more for 100% viewability?

Premium publishers are beginning to offer advertisers 100 per cent viewability – but of course it comes at a premium. Should advertisers have to pay extra for guaranteed viewability, something that many brands expect as standard? 
Of course the viewability discussion has been raging for some time, with two polarised views.
In June, Keith Weed, Unilever’s chief marketing and communications officer, said: “How much of an ad do [consumers] have to see before you pay for