That was exactly part of the point I was trying to make with the article. The other, that I left unsaid but should probably add explicitly, is that Slack et al.

That was exactly part of the point I was trying to make with the article. The other, that I left unsaid but should probably add explicitly, is that Slack et al. run on a server with a kernel, but choose to ignore the access control capabilities of said kernel and instead chose to reimplement them. I think it is a shame, and more software should strive to be security agnostic instead of reimplementing access control for the umpteenth time.