I think you missed the part where it says "(f) Disclosure to Committees of Congress
(1) Committee on Ways and Means, Committee on Finance, and Joint Committee on Taxation
Upon written request from the chairman of the Committee on Ways and Means of the House of Representatives, the chairman of the Committee on Finance of the Senate, or the chairman of the Joint Committee on Taxation, the Secretary shall furnish such committee with any return or return information specified in such request, except that any return or return information which can be associated with, or otherwise identify, directly or indirectly, a particular taxpayer shall be furnished to such committee only when sitting in closed executive session unless such taxpayer otherwise consents in writing to such disclosure."
you missed the part where it says "shall furnish". Not "shall furnish if approved" or "feels like there's a good reason." Shall. Furnish.
Now, funny story. This law was written to specifically give Congress the power to see a President's tax returns to make sure they weren't profiting from their position. You can thank Harding and the Tea Pot Dome scandal for that one.
Eastland V United States Servicemen's Fund. When the Unamerican activities committed subpoenaed the Servicemen's fund's tax information, the Fund argued that it was a violation of their 1st Amendment Rights. The Supreme Court said No. The intent of Congress did not modify their authority to subpoena documents.
Now, Watkins V US says that Congress does not have the right to expose other parties private information to the public it DOES have the right to see it in their oversight capacity.