One of the reasons that we are given for blessing same sex unions or recognizing that homoerotic relationship are blessed is that people claim to see evidence of God's grace in those involved in homoerotic relationships.
I believe that this is what I call Reverse Donatism.
Donatims, if you will recall, is the heresy that states only the sinless can be ministers of God's grace. It comes from the aftermath of the persecutions in the Roman Empire. The donatists formed a very ethically religious church that would not allow clergy who had caved during the persecutions to continue as clergy. They stated that the Holy Spirit had departed from them.
This later came to represent the idea that only the sinless can minister God's grace or have leadership positions in the Church. Of course, this is not an Anglican concept. We believe the God's grace works through sinful people and if it doesn't we are all in deep, dark serious trouble.
But here is how I describe Reverse Donatism.
Let's take the behaviour at hand - homoerotic relationships. It could be anything, but this will do. First, we say that we see God's grace active in the lives of people involved in this behavior. The next step is to say that this is evidence of God's blessing on the behavior. In between these two steps is the unspoken (and wrong) idea that God's grace cannot be present where sinful behavior is present, therefore, the behavior in question cannot be sinful.
Thus, since God's grace is evident in the lives of people involved in homoerotic relationships, the homoerotic behavior itself cannot be sinful.
Again, if God's grace cannot act or be evident in the lives of sinful people, then we are all in very serious trouble. The problem with this is that it sounds so good and "right" or logical to us. We constantly look for signs that God loves us and approves of us. To see the greatest sign that God loves us, we need to look only at the cross. To see if God approves of our behaviors, we need to learn to understand God's self-revelation in Holy Scripture and in the Natural Law and we need to do that in community - the larger the community the bigger the chance that we will correctly discern God's will for our actions.