I think I'd be slightly disappointed.
Not with my son, nor for him being gay, and I certainly wouldn't hold feelings against them for being gay, but I'd be disappointed that he might not have his own children.
I would also like a family line and my family name to carry on.
Myself and my two brothers are the first members of our family with our family name, and it would mean a lot to me if it could be carried on to children descended from me.
But at the same time I wouldn't be too upset if a gay son adopted children who took my family name. My own father was adopted and his surname, which is part of my own surname, comes from his adopted family and isn't derived from his biological parents.
I think really I wouldn't have a problem with a gay son.
But I would also like a son with a wife and children too.