The outrage expressed in the link seems to be that Tesco (and the likes of me, among others) aren't treating tomorrow with the same reverence that these Christians clearly do: can't see why we should though, and can't see how whatever the Tesco promotion is prevents these same Christians from spending tomorrow as they think fit.
I'm not sure I read it like that.
To me the issue seems to be that Tesco didn't recognise that their advert might be considered offensive to those who see Easter as a important religious festival.
I don't think that means that those who aren't religious shouldn't mark Easter and the bank holiday weekend as they wish. But I don't think that want to celebrate Easter in a non religious manner wish to cause offence to those that do, and that's the problem with the advert.
But, of course, those who are marking the 'real' meaning of Easter are those that are celebrating the spring and marvelling at the new life bursting into flower, wing and song all around us. And I suspect that include the vast majority of those who see Easter as a secular holiday, whether or not they overtly note it. Frankly it is pretty well impossible to fail to note the significance of the season, with longer evenings and new leaves and blossom all around.
And hence the challenge to the Christians - the older pagan meaning of Easter is obvious, needs no study or convoluted thinking. It simply 'is' and is obvious to all regardless of upbringing etc. How hard must that be for those that believe in the Christian version of Easter, which is (let's face it) completely unbelievable to pretty well everyone unless you are brought up to believe. If a message is only believable if you are brought up to believe, then it is a weak message indeed. Strong messages are as readily accessible and believable by all regardless of upbringing.