I treat paywall sites like books. They are perfectly fine references, and potentially great sources of information. But just like you wouldn’t insist that someone read Chapter 12 of an architecture book in order to understand your position in a discussion, you shouldn’t leave a link to a paywall site and expect that to be sufficient to make your argument.
If you’re using a book as a reference, you would want to quote some of the relevant text, or at least give an accurate summary of the information in the book that applies to the discussion. I’d expect the same if you are using a paywall site. And really, most of the time it’s better to do that for a link to a soft paywall site, or a site with no paywall at all so that people don’t have to track down what you mean.