There is no such onus. If you don’t want to go through a paywall, feel free to find an alternate source.
Again, not my job to find an alternative source. If someone is posting about an article, the article should be readable, and not be behind a paywall. Don’t waste people’s time posting news about articles that they cannot read, because its behind a paywall.
Or maybe mark them as such, as part of the title, at the very least, so that someone can not bother to click on the post link if they know they can’t get to the article that the post is about because its behind a paywall. Or supply an alternative non-paywalled link as part of the summary.
That’s the onus I’m speaking of, being able to actually get to the article the post is talking about. Don’t waste another’s time.