Why Slack may live to regret its smarmy letter to Microsoft

Slack has always been easy to like. The fast-growing team communication startup had a classic underdog story, with its founders falling ass-backwards into enterprise software following a failed effort to build a video game. It’s led by Stewart Butterfield, one of the kindest and most self-aware founders in Silicon Valley, who had previously given the world Flickr and then gone through the wringer after its acquisition by Yahoo. And it makes a genuinely useful product — the company ma