Critical time

What was the estimated mass of the island one colony? ABernal Sphere would come in at under 4 million tons, and a simple Space Manufacturing Facility could mass much less still It must be remembered that
even if launch costs from the moon + manufacturing & assembly costs for an
O'neill colony, are $10/Kg (1/1000th current earth launch costs, not including
the cost of assembly in orbit) a Billion tonne colony would still cost $10
trillion. This is equal to the GDP of the United States at present levels. Yes, we all recognize this argument. It's Bob Zubrin's, and he used in in "Entering Space" to convince everybody that those Gerry O'Neill ideas are crazy, so why don't we all ignore them and come back to these marvelous Mars ideas. Lift costs 1/1000th current ones certainly sounds like a generous assumption. But why should electromagnetic launch from the moon have any basis for comparison with launch via chemical rocket? The MIT study concluded lunar mass-drivers could lift lunar material for a cost of around 10 cents/kilogram. For Zubrin to successfully dispute this, he must identify the calculation errors in these previous studies, and not merely throw out a number of his own, no matter how generous-sounding.