Typically this is a Christian argument used against Islam - but I’m actually curious if this is seen as a valid argument from a secular point of view? (Even if it’s not the “best”)
Because essentially it’s “your holy book contradicts the holy book it claims to be endorsed by”, which personally I think I can see working on a secular level, even if you don’t actually believe in the Bible either.
spoiler
! Also, full disclosure: Yes, I am a Christian. !<
Not really keen to get into a theological argument about a sacred text I don’t believe in. However, if you gave a neutrally translated Bible to someone who had never heard of the Trinity, it’s extremely unlikely they would come to Trinitarianism on their own.