Here's a screenshot we took of that section. To note, citizens from 38 countries that don't need a visa to enter US soil have to apply for an ESTA.

As you can guess, the proposal was met with a lot of criticism from the start due to the privacy risks associated with giving your online usernames to the American government. The American Civil Liberty Union is especially worried that discrimination would "fall hardest on Arab and Muslim communities, whose usernames, posts, contacts and social networks will be exposed to intense scrutiny."

Sure the section is clearly marked "optional," but knowing how strict the US is in letting people in, most people would likely fill it out to avoid any hassle. Further, its critics argue that the US is setting an example that other countries might copy, putting more people's privacy at risk. The good news is that travelers aren't required to make their posts public, so they can tweak their privacy settings if they ever feel forced to hand over their social media usernames.