While true, that's not going to motivate anybody. Memory is not a very scarce resource, we're making more all the time, we can continue to make more, and it's reusable.

Moreover, memory that isn't being used is almost completely useless - the only thing it does is act as disk cache.

Better to use memory than CPU, as the latter actually consumes power (leading to climate change if not powered using renewables etc.) - although even better to use less of both.

A more effective argument would be to look at the number of users on low-end devices, and point out that, the more memory you use, the less these users are able to run your applications.

Not that I'm expecting companies like Slack to care - they design for the high-end user, and if your company forces Slack on you and you have an older device, there's nothing you can do, and they exploit that.