My friend and I had this same debate. She is for real trees and we have an artificial tree (10 years old). She argues the "stuff" used to make the artificial tree is most likely not good for the environment and after people are done with an artificial tree, it goes into a landfill where the plastic parts may never break down.
I argued that growing a tree, cutting it down and using it for 3 weeks isn't the best use of resources. But she pointed out that our city will pick up your tree at the curb (or you can take it to a park) and they will turn it into mulch which the city uses in the public parks and green spaces. So she argues her tree keeps on giving after they use it for a Christmas tree.
It's a toss up, we've decided. And I had to agree with her about getting rid of old artificial trees. Most are just tossed into the trash. A way to recycle them would be better.
But for frugality's sake, I won. I bought my tree for $40 ten years ago. $4 a year isn't a bad rate. She paid $30 for her real tree this year. That's $10 per week of use (maybe a bit less, she hasn't taken it down quite yet).