I typed up a response, but I ended up losing it all. Stupid internet.
Anyway, what I had responded was that if we aren't talking twinning, then that zygote that splits is still the same zygote. The zygote does split into two, then four, then eight then so on until after I think 16 cells it becomes a morula. That is why we have many cells now. We start out as a single cell but we have to divide to become multicellular.
With twinning, it is one life becoming two. Technically, the twin wasn't created from conception but without conception, that twin wouldn't exist. It's true that no one knows if that zygote will become two embryos, but that zygote is still alive and until it splits by freak of nature, it is an individual.