We certainly are all in agreement that curses are a staple of the Voodan faith. The issue was discussed when we implemented the domain, but following our usual guideline of remaining as faithful as possible to the source material, we decided not to grant voodans access to the curse domain. Three points to consider here.
1) As per canon lore, Voodans would not normally gain the benefits of divine domains anyway.
Each loa, in addition to three schools, also has three domains associated with it. The voodan chooses one of those three domains. He does not gain the associated domain ability, as a cleric would, nor does he gain extra slots per day to prepare domain spells.
2) As per 3rd edition canon lore again, Voodan do not get any bonuses to bestow curses. They gain the ability to create gris-gris, small token through which their spells are casted and that can be bestowed to others, as well as the ability to be empowered by their patron Loa. The fact that bestowing curses is common in voodan practices is by no mean an indication that they would have bonuses to do so.
3) We have not given up on eventually implementing the Voodan class itself. Limitations in the game engine prevent us from accomplishing it at this time, but with Beamdog freeing more and more resources that used to be hard-coded, there is still hope that we will be able to implement it in due time.