With a website / blog having thousands of pages and many thousands of external links, it is impractical to check external outbound link quality with any regularity. Informal link checks revealed that non-https:// websites had a substantially higher chance of becoming a defunct site that gets snapped up by spammers and scammers. To help mitigate some of the risk of websites going to unintended destinations, we decided to eliminate almost all non-https external links.
An increasing number of undesired websites are enabling https both to improve SEO and trick visitors. However, this additional friction anecdotally for the external links we’ve seen go bad has so far been rarer for https:// URLs. We have seen https:// sites be replaced by undesired content, but what often happens is the spammer doesn’t bother to setup the certificates correctly, so either the website won’t load if HSTS was used, or there are prominent warnings that the user has to click through.
There’s nothing to stop spammers from correctly setting certificates, but we feel https-only external links currently afford a meaningful benefit.