As far as i understood, the Problem with the Source is, that it draws attention to the Voidwoken, means even if you won't use Source for the "Evil" it makes attention to something which is "evil". Also if you look at the Prologue - it seems also pretty powerfull aka dangerous. However - maybe there is even more into it which will cleared up later =)
About Source Magic and normal Magic, i would say, the difference is between Ressource. In case of Normal Magic, it seems it uses Strenghts/Endergy within the Caster maybe Mana... like their own "energytype". Source however is an more defined Resource, which needs to be gathered specifically so you can use it.
was corrupted by the void dragon. This had been solved at the end of D:OS1. Why does the divine order hunt sourcerers several thouthand years later? I still do not understand what is the difference betwenn source magic and "normal magic".