You got mixed around on the first premise. It's not that preventing sincerity requires us to ignore unpleasant realities and tell small lies.
Instead, traditional norms requires us to ignore unpleasant realities and tell small lies, and this in turn prevents sincerity.
So, you're close but. But you had the first premise reversed.
If you'd like to see how I set this one up, you can see an explanation to this question at the following link:http://www.atlaslsat.com/forums/pt48-s4 ... -t743.html
Good luck with your prep! Let me know if you still have questions here.