"Mommy-hood": A choice or a title of distinction?

Today I heard someone say that you don't "earn" the right to be a Mom you choose it and that the celebration of Mother's Day was sexist. 

While working your fingers to the bone as a mother is certainly a choice, being called, "Mommy" is one of the most hard-earned titles in existence. We men constantly are told that there is a difference between being a biological father or "baby daddy" and being a "Dad." If being a "Mom" is just making a choice about having a baby, then that kinda tears down any argument the women who (accurately) say such things about men. 

Being a mother is THE HARDEST JOB in the world, and some would say, including me, that it's one of the most important (and currently one of the most poorly executed) jobs that the human race takes part in. I have been an at-home dad for going on five years now. I work very hard to keep my house looking like a home, but I've yet to do as good a job as my wife did at it. I work very hard to be the understanding, available at-home parent my children need, but I am at best adequate to the task (and sometimes not even that.) While I hope to be a good dad for my children, when my children scrape a knee or bump their head it's not Dad they call for. They call for Mommy.

People who argue the role of women in the home tend to devalue it by calling it merely the "propagation of out-of-date gender roles and sexism. I'll state for the record, however, that anyone who can say that the genders have no separate qualities and are in all things equal are not only devaluing thousands of years of women's toils (a rather callous and sexist act in and of itself), but are ignoring the vast majority of psychological research and evidence to the contrary. I would love to say that my work as an at-home father was equal to that of my wife but the fact that saying so would be convenient to my ego does not change the inconvenient truth of the matter. 

Now before I get a bunch of hate mail from single parents, let me say this: I'm not saying that a single parent such as a widower or divorcee can't provide a loving home for their children. I'm not saying that a man or woman cannot do a good job of raising their children by themselves. I AM saying that the all-important role of Mom is a role custom-fitted to the qualities women possess much more so than men. If you want to call me sexist on that point, then keep in mind that that statement was not critical of the professional qualities of women, but of the significantly smaller portions of motherly qualities in men.

While women can be and often are great/equal to/better than men in some professional outlets, the majority of women are and will always be better suited than men to the task of being a "Mom." In other words, you can choose to be a biological mother or baby-mommy, but only your children can decide you're worthy of being called "Mommy."