^At first glance, a truly wicked, stinging thing to say....but if you really examine the thought, I think it's what a lot of us (well, at lease me!) were trying to say.
OP, look at one of your existing two children. Now imagine giving one of them away as a gift, to a friend who is unable to conceive on her own. Couldn't do it, could you? Now, imagine that it is going to be any different to make a baby with your husband and give that baby away....it's not going to be any different to you...and because this baby is staying "in your circle", it may take a while....days, weeks+ for it to sink in, but I think it's going to.
The baby you make with your spouse would not be "genetic material" to you, in the end, any more than you would call one of your existing children your "genetic material". Seriously. Look at your daughter and say the words "There is my genetic material playing on the floor, what's so wrong with giving her away!" - she's not yours because you have had the chance to know her....she's yours because she has belonged to you since the first time you heard her little heart beat, isn't that right?
My fear is that you would trick yourself into believing this would get easier and easier to "get over" with time....so you would ignore the screaming voice inside of you and give the baby to your friend even thought it was really tearing you up inside to do so. Can you imagine watching your baby growing up as your friends child? That is the stuff of nightmares, right there. I can't imagine.