Indeed, Christianity likely holds that title, although due to the modernization of weapons and the growth of the overall population, secularism has surely killed the most people indirectly (due to guns, pollution, nicotine, etc). I've been thinking of writing an article to weigh the variables and determine which is the world's worst religion. The judgment would depend on the criteria, of course.

Having an insider's perspective on something can certainly be a strength . There are numerous very effective and instructive critics of Christianity who were brought up as fundamentalists or devout Christians, such as Robert Price, Matt Dillahunty, Bart Ehrman, and Paulogia and the Prophet of Zod (on YouTube). Those critics are very formidable, largely because of their insider's knowledge.

I was brought up as a Reformed (liberal, secularized) Jew. But I've obtained something that approximates an insider's perspective on Christianity by engaging so much with them and by stretching my imagination. I suppose it would be traumatic, though, to abandon one worldview for another. It would be like dying and being reborn.