Sadly, Goldman Sach has no choice but to comply if ever the IRS can find a court-backed order for any information from the clients of Poloniex. We have seen the same thing with Coinbase. Exchanges are there for the money and they don't want to get entangled with any government agency all because it can threaten their money factory. This is something we have to accept otherwise find another good exchange not under the power and influence of USA.
But what about the users outside of the US who are not residents? How would they be able to pay the IRS? They don't have accountants, some of them are only students, and I reckon many of the users are the people in this forum who are really from Asian countries, just by looking at how they speak English.
Also, when they say taxable, they mean capital gains made when you trade to fiat, right? Not bitcoin?