That’s only part of the arguement of necessity, that Mary conceived in her heart by the Holy Spirit, that they would be saying is not a good one. We have to take stock of God in this, that what He does speaks for itself and transcends what we might think a better arguement. Of course Mary’s Immaculate being is fitting, there’s no arguement there, not from that post there wasn’t; but it is not only fitting, it is actual truth. What God chose to do with Mary becomes necessary and if not then we could not find it at all fitting either.
Of course The Father could have done this and everything an infinite number of different ways, but this is the one way that He did it. This is something that when you speak to protestants about Mary’s Immaculate Conception that you may have found is near impossible to get them to see, but it is nevertheless true. They may feel that it is just as “fitting” for Mary to have other children, afterall she was a married woman and there is no sin there. You see, if you limit something as sublime as the Immaculate Conception of Mary to the realm of what is only fitting, then it is a highly subjective and precarious realm you limit her and God into; what if another thinks it more fitting that Mary should be very sinful? It at this point that we must understand the insufficiency of the idea or some might well say, the notion, of this being true because it is only fitting.
This idea does not really fit the bill, when you put Mary who is Immaculate because it is just fitting that she is so, you have empty space around the outline when put into perspective with the other doctrines, the Assumption (it is necessary that all flesh must die, but once, but it is not only unfitting for Mary to die it is impossible that she die). But the massive reason of necessity is of course, Jesus.
That is why Virgin Mary is the Best role Model after Jesus Christ, and the reason why she is Our Mother.