there are times when analogies are very helpful.. this isn't one of them. instead of comparing it to that, let's talk about what it actually is. an illegal black market for drugs. you're either being greedy, disingenuous, or crazy if you think their money should be returned. if anything they are lucky the government doesn't pursue the users with legal action.
The moment I transfer a bitcoin to Silk Road, it's no longer my bitcoin. It's theirs. I've exchanged it for a promise from Silk Road to pass on the bitcoin to someone else or return it to me when I ask.
The government never seized my bitcoin. They seized Silk Road's bitcoin. This means Silk Road has more liabilities than assets. And since Silk Road hasn't given me a promissory note in exchange for my bitcoin, I'm an unsecured general creditor - and unsecured general creditors cannot establish standing to recover seized assets.
It's not illegal pre se, but if the website is engaged in illegal activity subject to seizure, you may lose your bitcoins, unless you can prove it is not connected to illegal activity.
