Slack CEO Stewart Butterfield. kk / Flickr Stewart Butterfield, cofounder of Flickr and CEO of the office-communication software Slack, lashed out against a Wall Street Journal editorial in a tweetstorm Sunday night.

The Journal editorial in question addressed the recent killings of nine people at Emanuel AME Church in Charleston, South Carolina, saying the event was caused by a "problem that defies explanation."

President Obama had compared the shooting to the September 1963 bombing of a church in Birmingham, Alabama, that killed four young black girls.

But the Journal editorial says the comparison is inadequate: "Today the system and philosophy of institutionalized racism identified by Dr. King no longer exists."

Butterfield spoke out against the column's logic and ended by directly insulting The Journal's editorial board, writing "So, WSJ editorial board: f--- you!"