If people want to do their bit for the environment, there are so many things to target ahead of Christmas cards, which spread goodwill to others, aren't there?
Why is it that so many people suddenly want to appear interested in saving trees and fuel at Christmas, yet all the rest of the year, they buy themselves cardboard-packed sandwiches and food products, out-of-season food from overseas, magazines/newspapers they could have read online, they don't ask people not to send them birthday cards, they buy non-essentials like wine (why not think of the enormous waste of glass, and the fuel miles, for a drink with no nutritional value?), they take the car to work instead of lift-sharing or using public transport, etc. etc.
It's ostentatious and worthy to announce you're making a charity donation. Why don't people give to charity quietly and privately, instead of using the no-cards thing as an opportunity to proclaim their own charitability? (And how charitable is it really, when it's money you would have otherwise spent anyway?)
Best to donate instead (without forfeiting someone else's Christmas card or announcing your donation) at another time of year when the charities aren't receiving everyone else's Christmas donations as well. Same goes for soup kitchens who don't need all these charitable-for-one-day types on Christmas Day/New Years Eve as everyone else wants to help on those days too - and then go back to normal life for another year.
Sparkling I do agree with you on cards featuring people's children. I'd like to celebrate Christmas, not other people's fecundity. Can't stand the Round Robin smug-fest either. But these are in no way essential aspects of card-sending.