Wait, what? How would adding an indication that the article is paywalled inhibit/hamper support for high quality content?
If an article is paywalled and I don't have any indication about this, I would open the link, notice it's paywalled and then decide whether to pay or not. If a tag is present, this just moves the decision early in the process.
So, again, how would not using such a tag help support high quality journalism?