Check out the blog "I Look Down on Women with Husbands and Kids and I'm Not Sorry" by Amy Glass, and you will have no doubt.
In a word, it is selfishness.
This poor woman has no idea what real happiness is, which only comes from devoting oneself to others. She may experience the thrill of accomplishment that comes with a big job and lots of money, but we run-of-the mill moms know what a temporary satisfaction that is.
Real happiness comes from sitting with your six year old and hearing her successfully work out a word that you know she has never seen and isn't even phonetic. It comes from planning and preparing your husband's favorite meal when you would way rather take a nap. It is found in organizing your son's messy room so he will grin with delight when he comes home and can find all his lego figures in one place. It is in remembering on your way home from the store that your daughter asked you to buy some ridiculous snack and turning around to run in and get it just to please her.
True joy is watching your child turn from a newborn into a person with a beautiful and generous character. It is overhearing your 5 year old praying for other people. It is in sharing the peace of Christ with someone who was previously missing it. It is knowing you made a real difference in another person's life.
Sorry to tell you, Amy, but backpacking through Asia by myself is not even on my list. It would be a complete waste of my time, which is far better spent walking the dog with my family. You say, "You will never have the time, energy, freedom or mobility to be exceptional if you have a husband and kids." I couldn't disagree more. We wives and moms ARE exceptional to our husband and children. Irreplaceable, really.
You may accomplish great things during your life as far as this world is concerned, but at the end of it all, you will find yourself with the only thing that has ever been important to you: yourself. Your work will disappear with you at the end of your life, but the work of us "average" moms will live on for eternity.