I’m 90% sure if Mal had survived through the plague in lordaeron and not been infected with the other priests of the church he would’ve became a scarlet (not just because his ex joined them). Even after he was raised he had very negative feelings towards the undead and being one himself. He, among others, believed it was a sickness- wanted to believe that anyways. Eventually he came to the realization and acceptance there was nothing that could be done (and the undead weren’t all bad) so now he just is how he is.