Without going too deeply into the Halbig decision, the basic premise that is being argued by conservatives is that the law means what it says. The law unambiguously dictates that subsidies are available only to State exchanges created under section 1311 (Federal exchanges were created under section 1321). As such, policies secured through the Federal exchange shouldn't get subsidies. This presents a particular problem for Obamacare, as it means that millions of people would be exempted from the insurance mandate because their policies would become "unaffordable" under another section of the law.
The left is up in arms about this, first claiming it was a "typo" that it didn't include a provision for Federal subsidies. Sean Davis thoroughly destroys the "typo" argument here and I'd never assume that I could do so any better, so we'll move on.
The left has now drifted to a new position of "intent" of the lawmakers. They point to some earlier drafts of the legislation that point to both Federal and State subsidies as to how we should interpret the existing law. This might be a relevant argument except for one little fact: the final legislation passed by both houses of Congress and signed by the President is clear that subsidies are for State exchanges. Intent matters only insofar as how the law is created, not the results. To use a line from Dan McLaughlin: As far as statutory intent, the law means the same thing even if Harry Reid thought it gave everyone a pet unicorn. For a more complete debunking of this theory see Charles CW Cooke's article on the National Review website.
Here's an thought experiment for you: suppose that there is a law being debated by Congress regarding immigration. The White House along with dozens of outside consultants are contributing to the drafting of this law. One initial version says that all 10+ million illegal immigrants should be granted full citizenship with no fines and full voting rights. A second version says that they should be given provisional visas and have to pay a fine. A third version is the same as the second but only includes those under age 25 who came to the US as a minor. So here we have three drafts circulating with some similarities but also several key differences.
Congress passes and the President signs into law a bill that says that all illegals under 25 (part of #3) can get a provisional visa (part of #2) and not have to pay a fine (part of #1). Now suppose that US Citizenship and Immigration Services (USCIS) decided to grant full citizenship to that group because it was the intent of the lawmakers. Would that be legal under the legislation that went through the Constitutionally required process? Or did USCIS unilaterally take an action that was outside of the law?
If you look at that scenario and believe that the law wasn't followed then I congratulate you on your understanding basic civics. If you look at that scenario and believe that the government should be able to do whatever it wants based on a discussion or draft that didn't get signed into law, please watch this brief YouTube video that I think will help you realize your problem.
What is laid out above is a perfect analogy what happened in the case of Obamacare. Whether intended or not (which we'll never really know since all of the negotiations were done behind closed doors, breaking the President's promise that they would be on C-SPAN), the law was signed saying subsidies apply to State exchanges and the IRS is giving subsidies to those on Federal exchanges without authorization.
I have challenged several prominent liberals on this point and will extend the challenge to anyone who cares to answer:
If we look to each proposal offered in the drafting of legislation instead of the the law as passed, would a future GOP President be able to abolish Obamacare because there have been amendments offered by the GOP to do so, even if they didn't make it into any final bill?