That's elementary: Since SR was the only place where owning BitCoin was actually useful since you couldn't buy using dollars and was a big market (in turn-over), it's seizure by the FBI should driven BTC price down because the largest btc-related goods trader closed, so all those people buying illegal products, would stop searching/buying for bitcoins. Simple as that.
So losing 40% to 50% of it's value should be expected/rational, IIRC lost from 10 to 20% for a couple of hours. The senate thing you're referring happened later on and it's still NOT clear how will end.
Then you go making an assertion... Like if anyone really cares if you buy drugs, guns or chocolate with your currency. The world doesn't work like that, no one bought/used BTC because suddenly became ethical to own one since the good BFI caught the bad Silk Road guys. If that was the case, the USD wouldn't be so widely used.
Out of curiosity, you think that Adi Shamir is wrong?