Which is more problematic, ordaining a homosexual man or ordaining a woman? To ordain someone who sins publicly and without repentance would be a scandalous failure of discipline and Biblical fidelity on the part of the church body. And yet, there have been homosexual pastors before. No one has denied that, whatever their sin, they are true pastors and that the sacraments they administer are valid.
To question that would be to fall into the heresy of Donatism. A Lutheran cannot hold that position. The Augsburg Confession, Article VIII, says of Lutherans that “They condemn the Donatists, and such like, who denied it to be lawful to use the ministry of evil men in the Church, and who thought the ministry of evil men to be unprofitable and of none effect.”
In the case of women, though, the question is whether they can be pastors at all. If not, their orders are illegitimate. That would seem to mean that the sacraments they administer–with the exception of Baptism, which can be performed by any layman–are invalid. (Question: Is that the position of those who reject women’s ordination? Or since the keys are held by the congregation, can the congregation have valid sacraments no matter who the pastor is?)