I think many people would believe that abortion is murder without being religious. That is not now the case about the seven day literal creation, but it was either the case in the past, or the account in the book of Genesis was not believed by the author, or not intended literally, since it was written one way or the other.
But in any case, again, Lewis adopted his religion as an adult and might not have adopted it if it had contained arbitary content such as "eating mushrooms is a grave sin that will be punished by a worse hell than anything else." So even if we falsely assume that the content of all religions is completely arbitrary in itself, the content of his religion would not be, since he chose it.
I think many people would believe that abortion is murder without being religious.
That link shows that one person would believe that abortion is murder without being religious. A poll shows 84% of atheists and agnostics in favor of legal abortion, with 14% against, and even that 14% is not specifically about zygotes, it's about abortion as a whole.
But in any case, again, Lewis adopted his religion as an adult
His family was Anglican and he became an Anglican. That suggests that he adopted the religion mostly because of the influence of his background.
Another month, another rationality quotes thread. The rules are: