This week, representatives from Google, Twitter and Facebook all spoke at a congressional hearing about how they present news and opinions on their platforms. The next day, Facebook's Mark Zuckerberg told the Recode podcast that Facebook shouldn't overregulate speech on the site, even if it means not banning Holocaust deniers. So how much should these companies be responsible for what is said online? Sounds like a good Quality Assurance topic, the segment where we take a deeper look at a big tech story. Marketplace's Molly Wood talks with Mike Nuñez, editor at Mashable.