I used to be with the SSO-wall-of-shame crowd...until I had to maintain and support SSO within a production app. G-suite/Social SSO? Fine. Not a problem. SAML? Good luck automating that and not having to reset certs / tweak things per-client. That's why it costs money.
Another problem I have with the "SSO should be free, because it's security-related" argument is that it's a misunderstanding of why it costs money. It's not because companies want to gate security features. It's because when you're trying to create a pricing model for an otherwise free product, going from "I'm ok with manually inviting/deactivating users" to "I now need SSO, because this product has enough adoption within the company to merit it" happens to be an almost a perfect way to delineate between casual freemium users and business users who should be paying. That, combined with my initial point, is why I dropped out of the SSO tax crowd.
Another problem I have with the "SSO should be free, because it's security-related" argument is that it's a misunderstanding of why it costs money. It's not because companies want to gate security features. It's because when you're trying to create a pricing model for an otherwise free product, going from "I'm ok with manually inviting/deactivating users" to "I now need SSO, because this product has enough adoption within the company to merit it" happens to be an almost a perfect way to delineate between casual freemium users and business users who should be paying. That, combined with my initial point, is why I dropped out of the SSO tax crowd.