That's true, but why does that mean they need to shut down her account just because she visited Cuba? Would that mean a grocery store would then have to refuse to sell you their goods because you visited the country once?
The guy's wife didn't do anything wrong. Slack broke the law by providing an embargoed service to someone in Cuba. I'll bet money that when this was discussed with their compliance officer, the lawyers and engineers and everyone else agreed to use certain metrics (like source IP) to determine whether someone fell under the embargo. Otherwise, Slack would have to spend a lot of time and money validating people's identity, etc., in order to comply. I don't really fault them for taking this path because their exposure is huge and compliance is hard.
Your analogy about grocery stores doesn't really work because logging into Slack isn't the same thing as walking into a grocery store, because buying from a grocery store isn't the same thing as exporting food across a national boarder, and because neither food nor medicine is embargoed.
They didn't shut down their account because she visited Cuba, but because her account was created _from_ Cuba. It's unfortunate but I guess it's the only way Slack has to "know" where an account is from.
They should never have allowed the account to be created from Cuba in the first place. Slack when it was younger, didn't have good policies in place to actually follow US law. As such, now that they are reviewing their old records they realized they committed illegal actions that they need to clean up.
Yes, it harms their customers, but that harm and the resulting damages to Slack' reputation (and maybe legal costs), is what they must pay for being negligent in the past.
Your analogy about grocery stores doesn't really work because logging into Slack isn't the same thing as walking into a grocery store, because buying from a grocery store isn't the same thing as exporting food across a national boarder, and because neither food nor medicine is embargoed.