Swearing on a Sagan book is arguably better. It's based on fact, not an unverifiable and highly unlikely fairytail.

* fairytale

Fairies don't have tails.

Science is not a source of mores, it’s about observing facts.

To the true believer a religious text is considered as factual as any scientific work, so that isn't really as much of a differentiating factor when you think about it from their PoV.

I’m not saying that religious texts are non-factual, I’m saying scientific texts have no moral implications, they ONLY lay out material facts.