Consider the split in the CofE over women clergy. Roughly half believe God favours the liberal stance, the other half believe the traditionalist view. In casting their votes on the matter, these people are expressing their view of what god wants. This is nothing to do with self interest, these are people split over a theological issue and they cannot all be correct. If what you claim were true, then God would intervene to correct christians who were expressing a mistaken witness to God's will.
A bit of clarification is needed here. There is a difference in discerning God's will and proclaiming that God has asked you personally to do something in His name. The former is not an exact science and is open to various forms of corruption and mis interpretation. The latter can only de done by a genuine Christian under God's influence, or someone who is totally deluded and under the influence of something evil.
Just remember that this bit of discussion was started by Flo asking if I would kill one of my children if I felt certain that God was asking me to do it. It is not about discernment of God's will, but obeying His direct orders. As a Christian, I do not believe that God would allow me to mis interpret a direct order.