YANBU. I love sending and receiving cards. Christmas in your own bubble without reaching out to friends/family far and wide would be different IMHO.
A kind gesture which gives pleasure to someone else is not a "waste" just because it happens to be made of paper or card.
It reminds me of the Bible story where a woman poured perfume on Jesus and people criticised her for "wasting" it.
"Some of the people there became angry. They said to one another, “Why waste this perfume? 5 It could have been sold for more than a year’s pay. The money could have been given to poor people.” So they found fault with the woman. 6 “Leave her alone,” Jesus said. “Why are you bothering her? She has done a beautiful thing to me. 7 You will always have poor people with you. You can help them any time you want to."
There are so many other things made of paper (or not), which people don't seem to want to give up in order to donate to charity quietly. Newspapers, coffee in a paper cup, magazines, postcards, wine, meals out, sandwich packs in cardboard, etc.
Charity giving should be done privately, not announced to others.