> I'd be forced to use their awful client
Who forces you ? You can use slack on the web can't you ? You don't need to have yet another browser engine running on you computer.
> Just use IRC.
Please don't … IRC is the opposite of user friendly: it has no good web interface so the casual user won't come in because he doesn't want to install and learn a new software (IRC client). But slack isn't the only option here, it's not even the best open by far, Gitter[1], Mattermost[2] and Discord[3] are alternatives to IRC which aren't Slack.
[1]: https://gitter.im/ [2]: https://about.mattermost.com/, they don't provide chat hosting but several organisation do host mattermost servers (Framasoft for instance https://framateam.org/) [3]: https://discordapp.com/ targeted at gamers, which is a good sign of quality, but fine for general purpose use.
