There's a serious issue with Coinbase here. If this is true, we shall boycott this company immediately. I understand that the FBI or other law enforcement agencies can track your acts, or business, but Coinbase shouldn't. I want to point out that when buy drugs with cash, US dollars, nobody sees the Bank of America, nor the Federal Reserve as having been part in your wrongdoing. Coinbase customers should be entirely free to do illegal things with BTC, and Coinbase has no right to prevent its customers from doing so, nor should it track its customers.
That Coinbase.com does this is fairly well documented. They actually follow your coins, it is not only in cases where users withdraw coins directly from coinbase to a darknet market or gambling site.
And they don't only freeze accounts for those uses. They also flagged a bunch of accounts for simply making donations to people such as gwern (gwern.net, he writes and publishes research about the darknet).
Obviously it would NOT BE SMART to donate to our site from an address linked to a coinbase account!