It could be easily justified as there being a necessity to understand and counter necromancy as a growing threat. Much like how it works in other MMO's such as World of Warcraft when it comes to its versions of darker arts. It wouldn't the first forbidden power that the player character makes use of during the course of their adventure and with the likes of Y'shtola having used forbidden spells in order to cheat death not only for herself but for the sake of her allies as well then the lines between what is acceptable and what isn't become quite blurred.

It'd make for some interesting story elements if handled well and further broaden the game's appeal in the process. Especially when the game starts to move away from Hydaelyn and the limitations the Blessing of Light/Echo bring with them!