If you don't want to send Christmas cards, because you can't be arsed/ think it's bad for the environment/ just don't fancy it/ find it meaningless, absolutely fine.
But please don't go on social media declaring that the reason you're not doing it is so you can give to charity, and act all holier than thou about it.
Especially if you're constantly showing off your spending on nights out, clothes etc, so maybe some of that could be used for charity donations, and you're definitely affluent enough to afford a few stamps as well as a couple of quid to Save the Children.