Lot of misinformation going on here.
When the FBI seized the Silk Road Servers, there was about 30,000 BTC confiscated that was being used to fund operations. This is not the same BTC that they found on Robert Ulbricht's personal wallet. That wallet was over 150,000 BTC. Ulbricht has claimed that he earned these BTC legitimately and has contested their seizure. Therefore, the government can not sell these coins until proving Ulbricht earned them illegitimately in a court of law.
SOURCE:
http://www.theatlantic.com/technolo...als-are-selling-2965651306529-bitcoin/372770/
The coins that are being auctioned are the ~30,000 seized from the Silk Road servers. Nobody has made a claim that these are from legitimate activities, because doing so would directly link whoever makes this claim to the operations of Silk Road itself. Therefore, these coins can be auctioned off by the FBI.
The announcement of this auction lead to a decline of 10-15% in Bitcoin price. While it sounds like a lot of Bitcoin, most people would be surprised to realize that miners create ~3,600 BTC every single day. The amount of Bitcoins being sold by the US Government equals only 8.3 days of Bitcoin production.
https://blockchain.info/charts/total-bitcoins
There are approximately 13 Million Bitcoins in the world. 30,000 BTC represents ~0.2% of the worldwide supply of BTC. However, this does not account for BTC which has been lost through the years. 30,000 BTC may be closer to 0.5-1% of the amount of the coins which are actively owned.
Regardless, price impacts from these types of sales are often over reactions. A sale of ~$19 Million USD in BTC by the US Government on assets which were knowingly seized ~1 year ago should not drop the value by 15%. The sale also sends a signal to the market that the US government views Bitcoin as a legitimate asset which can be bought and sold.
So this was a good time to increase your position IMO. These coins will be sold to private buyers who are spending millions at a time. To buy these coins in bulk and attempt to resell them on the open market would not be profitable. People buying these coins are looking to hold. The purchases have the safety and security of being done through the US government, which is much more attractive than wiring millions of dollars to Slovenia (Bitstamp) or Bulgaria (BTC-e). There will be no shortage of big name buyers who will be looking to open / increase their position in Bitcoin.