You are absolutely correct. But wrong to assume that Dobson does not say these things.
It was the very fact that he saw marriages falling apart and children being hurt by their destruction, that motivated Dobson to form "Focus on the family".
One of the big problems faced by pro-family conservatives is that they are often portrayed as hateful scape-goaters. Although it is the left that, in fact, more often engages in hateful scapegoating, it is conservatives who, in many people's minds, are associated with it.
I think, therefore, it is important to cast arguments against homosexual marriage in a way which cannot be misconstrued as being hateful to homosexuals.