I have no doubt that some people feel called to adoption. I am not one of them. Neither is Husbandido. (I asked.) We talked about our ideas about how to raise children and how many children we wanted on our early dates; adoption didn't come up until we were well into the realm of infertility. (For those counting, think four or five years later.)
For us adoption is a choice; we may not like our options, but they seem to be a) adopt or b) remain childless. I am much more okay with b than Husbandido is; I keep trying to convince him that we should sell our 4 bedroom, 2 1/2 bedroom house and move to a cute little bungalow or cottage. No dice on that one, though; he really wants children. It's not that I don't want children, but I have more doubts and qualms about adoption than he does. At this point, we have more or less agreed to pursue adoption once we are done TTC. (Meaning in a month or two.) But for us, adoption is a choice, not a calling. It doesn't mean we are any less suited to adopt; it just means how we are getting there is different.
I don't quibble with the statement that not every couple who cannot have children should adopt; not everyone wants to do so or is suited to it. I also agree that adoption solves the problem of childlessness, not infertility. But I do think we need to be careful not to overemphasize adoption as a calling, as not everyone who could or should adopt may feel a distinct calling. Whether you get there via a calling or a choice, adoption is valuable and needed; every child deserves a home and parents.