I absolutely support this statement. It is a far better proposition to distribute these seized bitcoin among the community of less privileged people. Or even donating such amount to global organizations who works for the betterment of the society. But US is just trying to fill up their own reserve.
It entirely depends on the price of auction. If they auction the bitcoins as per the market price, we may see dumping. But it is highly unlikely to happen. Usually in such auctions, things are sold with a premium. If this happens, they we would not see dumping right at this point. So it depends!