[0] There's an argument to be made for depressive realism that would say I'm pointing out how things really are, but I'm not going to make it because there's also thousands of years of philosophy that makes a compelling argument for reality not being so easy to pin down anyway.
[1] It occurs to me that the seemingly increasing rate of depression in a lot of developed nations may be due, like almost all of society's ills, to advertising. Advertising confronts us constantly trying to get us to do things we don't want to do, namely spending money on shit we don't need, and so we develop a defense mechanism. That mechanism takes the form of a contrarian inner voice that argues against the bullshit advertisement telling you you'll be happy if only you buy whatever it is it is selling, but the contrarian voice doesn't have an off switch and recognizes all the little sales pitches of every day life as a threat too.
I think we're in agreement that a depressed person generally doesn't want to be cheered up and won't be receptive to it, so you can be positive as much as you want and it won't do much.
I've been on both sides of this, and as the depressed person it seems most helpful to remember that I need to put in the extra effort to try to be positive especially when I don't want to. And as the partner it's helpful to remember that you need to create some separation so you don't get too pulled in and then are unable to help in any way.
Psychologist has been fighting such social stigmas for decades.
I'd also add that (again maybe just for me) it's a way more helpful way to view it. It helps me recognize when I need to just go through the motions of being positive until I can get back to doing it naturally. It usually feels a lot better in the moment to focus on the negatives but somewhere in my head I know that's not going to help me.