Nothing to do with self respect This is a completely accepted and promoted way of growing your product. See for example the strategies outlined in “crossing the chasm”. Techies are in this case the early adopters, and now that slack has crossed the chasm, they are targeting a completely new user group, the early adopters, with a new set of needs and wants.
Time to move to a new product which still focuses on techies.
As a member of user minorities - the "tech savvy" niche and "knows software can be ergonomic, and expects that" niche - I'm already avoiding using new "innovative" products. The story is always the same - people with needs are used as tools to drive initial adoption, and then the product self-destructs trying to chase the lowest common denominator.
FWIW, I wouldn't even be using Slack if I weren't forced to, like probably most of its users. Regular employees don't have much say in what companies use for chat, nor do most people in communities in what tool was used to start them.
Time to move to a new product which still focuses on techies.