We exist because the timeless God desired fellowship. Fellowship>creation w/ free will>sin and judgement, but also heaven and love.
Although I realized that this question puts our mortal flesh on God, I think it is an important one:
If you knew for sure that, if you had children, you would have...
There is an important difference to make between the human structure created by fallible beings and the will of God. Just because one has obvious problems, that doesn't effect the other.
As a Christian, I can admit that slavery did exist during scriptural times, but you have to compare scripture to scripture. All of the religious laws that took slavery into account were there to limit the evils of slavery. On the other hand, you can find abundant evidence in the Old and New...