Personally; I can forgive an IDE, depending on what I'm doing (just viewing source shouldn't be spinning my fans).

But debugging, deep code inspection and so on are complex features used by specialists.

Slack is designed to be used by everyone; thus I don't give it as much of a pass. Because if everyone in my company is using a CPU core and 1GiB of memory to just talk to people then that's a very high actual cost of resources.

Just like you can forgive specialist software in other areas (final cut, photoshop, CAD) taking significant resources.

Tools designed to be used by everyone should be lean, optimised and feature complete. In my opinion.

You're not crazy. I feel the same. Similarly, I was beginning to think that I was crazy.... As another pointed out, I give a pass to heavy applications like my IDE.... but when my shopping-list app is using a Gig of memory and spinning up my fans, then I want to gouge my eyes out in disgust.