I disagree: Slack tends to be used by work-related groups, where people are already semi-prepared for what any one of their co-workers might post in the company

I disagree: Slack tends to be used by work-related groups, where people are already semi-prepared for what any one of their co-workers might post in the company Slack channel(s). Facebook is absolutely correct in keeping a very tight rein on this stuff, and in making the options uniformly "cute". If emotions start running too high, people will start abandoning the entire platform, I think.