But to clarify, they gave a service to people/teams who maybe they shouldn't have. Did the people signing up/using Slack know that? Maybe. Who's responsible to ensure it's enforced?
This is not about blocking accounts of people in Iran, which is a totally legit thing to do. This is about blocking someone who is of Iranian origin, but claims to live in Canada for years and has no business connections with Iran whatsoever. Probably it's some automatic filtering hitting a false positive, but question is how that works, what criteria they use to search for "suspicious" accounts? Have they been given the list of accounts by some US agency or they track and profile their users? There's a lot of confidential business info floating through Slack channels, so it's a huge deal for all of us if they data-mine on that in some way.