The other way of looking at it is that it can boost publication revenue and journalist income by driving more traffic to the publication than it would otherwise

The other way of looking at it is that it can boost publication revenue and journalist income by driving more traffic to the publication than it would otherwise get, of which some may convert to subscriptions (if the publication can offer sufficient incentive). Obviously, no user would be able to justify buying subscriptions to every publication linked from HN. And if there was no paywall bypass, then HN couldn't link to it and it would get no HN traffic and no discussion on HN at all. Allowing paywall bypass means the publication gets the HN traffic and discussion it wouldn't otherwise get, and the possibility of converting some of that traffic to subscribers who wouldn't otherwise subscribe. For what it's worth, the owners/operators clearly don't think it puts this forum at risk, as the sharing of paywall bypass links is explicitly allowed/encouraged according to the guidelines and moderator comments. And the very fact that the publications themselves allow bypass via certain referrers (e.g., Facebook) suggests they don't have a problem with it.