Mostly to "check my ethics"... what would I do if I were an 18 year old male soldier in Afghanistan, for example.
I will never be 18 again, there's no way in hell I will ever be a soldier and I am not a man. But thinking through situations and what I might do is helpful for me to try to flesh out my ethics, to help me keep my empathy and think about the motivations of others.
It is NOT offensive for a man to try to think of what they would do in that situation. It IS offensive if you were to say that you would never let any woman of yours have a baby with DS. Then, you're just being a controlling ass, instead of the way you put it which is 'how would you feel if you were in that situation?", which is an attempt to be empathic.
The alternative is that we would all have no empathy, which basically means we are all sociopaths. As a previous poster said, you never know exactly how you would feel until you are in that situation, but to me, trying to think it through actually helps me to try to understand others, their unique situations and to feel, just a little bit, of what they MAY be feeling. There are some situations so foreign to me that I cannot understand motivations at all (serial killers come to mind), but just about every thing else - trying to think how I would feel in that situation has led to me a little bit more understanding.
Besides which, while you will never be pregnant, you will (or maybe are) a parent. It's not that much of a stretch to try to understand how a woman feels about parenting. I personally think that men feel a lot more than they are "allowed" to. If a woman has a miscarriage, for example, no one ever asks how the man is feeling, and excepts him to just be stoic and strong, even though it was his baby, too. Of course, I am not a man, so all I can do is imagine that men hurt just a much as women when when lose a baby... but that's an attempt at empathy.
*this is my opinion only... others may have different opinions.