Why must uniquely- LDS Biblical interpretation be rejected?

Because a supposedly Biblical doctrine that is based on possibly-plausible possible exceptions to other historical doctrines is not a firm enough foundation on which  believers in the rest of the Bible should abandon Christianity.

For more information, see The Mormon Mirage 3rd Edition:  A Former Member Looks at the Mormon Church Today (Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.