The question is a mental exercise, justify gay marriage without using an argument that could just as easily apply to polygamy or incest, or alternatively, justify marriage between a man and a women where that particular union can't reasonably expect to produce offspring in a fashion that wouldn't equally apply to gays or incestuous unions, hence the reference to procreation. The primary point being of course that most of the arguments for or against gay marriage can apply to deny other standard unions or permit ones not currently allowed. Hence the question "can anyone justify gay marriage without justifying polygamy or incest and without mentioning procreation or two?"