From its earliest days, Silicon Valley has been animated by near-absolutist understanding of free speech. Other than exceptions for fraud, pornography or specific threats, the prevailing view among many tech platforms has been to allow pretty much anyone to post pretty much anything. These sensibilities are even enshrined in American law, which gives companies broad immunity from prosecution for what their users post.

But now, for good reason, the absolutist ethos is over.

Over the past two years, pressed by lawmakers and the media about the harm caused by misinformation, state-sponsored propaganda and harassment, tech platforms have begun to radically overhaul their attitudes about what people can say online and how they can say it.

Last week, Facebook announced a new plan to remove misinformation that it determines might lead to imminent harm. And WhatsApp, Facebook’s messaging subsidiary, said it would limit how widely messages on the service can be forwarded as a way to slow down viral rumors, some of which have led to mob violence in places like India.

The new policies are part of a larger change. Online services — not just Facebook but also Google, Twitter, Reddit and even those far removed from news and politics, like Spotify — are rethinking their relationship with the offline world. They are asking themselves a basic question: Where does our responsibility begin and end?