Last week, the Knight First Amendment Institute urged Rep. Alexandria Ocasio-Cortez (D-NY) to unblock critics on Twitter. The Knight Institute has led a push to treat politicians’ social media accounts as public forums, filing a successful lawsuit against President Donald Trump for his Twitter-blocking habits. Ocasio-Cortez argued that the issue was more nuanced, though: she said she was blocking “less than 20 accounts” and that it was for harassment, not political viewpoints.

Whether that’s accurate, the law suggests that blocking should be a last resort. A legal ruling from last year encouraged politicians to use Twitter’s “mute” function, which lets someone simply avoid seeing tweets from a user they dislike. It’s a fair way to protect the First Amendment online. But if the goal is to actually encourage meaningful speech, this hands-off approach raises real problems — even if it’s ultimately the right legal approach.

Court rulings against Trump have emphasized that his tweets’ reply sections create an “interactive space” that’s accessible to millions of people. Anybody who clicks on one of Trump’s tweets can see the replies, and, taken together, the responses function similarly to an offline public town hall. Trump isn’t required to read anybody’s messages, so he’s free to use the mute function, which just hides people’s tweets on his personal timeline. But blocking somebody would prevent them from seeing or engaging with tweets. And politicians generally can’t deny people the right to amplify their voices by replying to a social media post any more than they could kick them out of a meeting for expressing an unpopular opinion.

Social media poses some unique problems that physical spaces don’t, however. It can operate at a scale that wouldn’t be possible offline, and it’s easy to hijack a conversation or amplify a point of view with automated posts or a handful of dedicated people acting in bad faith. Trolls can attack anyone who participates in a conversation, not just politicians, and they can do it across all of social media, not just in a single thread or post. This can turn supposedly open spaces into deeply hostile or unnavigable ones — not just for public figures like Trump or Ocasio-Cortez, but for anybody who wants to engage with them.