The Infinite Number of Forms of Largeness

There are an infinite number of forms of largeness, not just one. This is the most famous criticism plato opposes to his own theory. But it's not immediately clear why it is so damaging. It's not like we'll run out of places to put them - given that large or not, they are immaterial. The problem, i think, is that socrates has placed so much emphasis on the idea that each form is one.