Please elaborate on "questionable corporate behavior". Everything else you said is matter of opinion and slack's growth would speak to the exact opposite.

"no encryption" - There is encryption, not end to end but data is encrypted at rest: https://slack.com/security

"horrible clients" - I disagree. They're not perfect but they work and are consistent 99.999% of the time.

"mistreatment of irc users" - People need to get over this. It's not IRC. That's like being upset that email doesn't support fax well enough.