Another is that they just started putting light-grey text "Message @channel" by default in the text area. I am surprisingly stressed out by this. It feels like a command or a nudge that insinuates itself into my thinking space, like a half-finished message which a corporate entity 'helpfully' began for me, and now it's my job to finish it, and as soon as I finish that one another will begin. There's a bad dream in there somewhere...

I think the OP is right that a UI needs to be sensitive to the user's psyche and not push them all the time toward using the product.