"Explain to me how I threw up a straw man by responding in this manner."
Sigh. All right.
The point of bringing up your nieces was to try and get you to think about the matter in the context of females with regard to whom you might feel protective, females you not only know and like, but with whom you have blood ties.
I could have posed the question in terms of wives, but daughters and nieces tend to be younger and more innocent, and therefore more in need of protection.
I was hoping, futilely, that you might reflect, "Gee, if the women I care about deserve protection, then the women other people care about do too."
Guess not.
My argument was never about incest in any way, but about protecting your nieces from exploitation by *other* men. I was actually surprised when you brought up the subject of incest, because it had never entered my mind.
Your setting up and knocking down the incest argument was, therefore, a straw man.
No, it was an answer to your question. You simply expected me to respond in a different way. You might want to check out this: Straw Man.