I've suffered with some pretty hardcore depression. To me, depression itself isn't necessary something to be angry at it, it just "is" -- it's something that some people just have to deal with. The stigma attached to it still (although things have improved a lot since, let's say 50-60 years ago) is still negative... mostly when people don't understand it, so they take it to be laziness or defeatist or whatever. Things actually look very bleak when you're in the middle of it and even when you feel sane.
However, I do find myself irritable (moreso than if I hadn't had a history of depression) when I sense a truly defeatist attitude. I had to learn to take care of myself, in order to get through the depression, and I can tell the difference between someone who is trying to figure things out but is just confused and waylaid by the depression vs someone who has just given up completely and isn't even bothering anymore. This certainly doesn't mean you're supposed to "be chipper" and "perk up," that's unrealistic, or that you'll always have energy to make continual progress; but there are those looking for a way through vs those looking for an excuse, and now especially after I've been there myself and was tempted to give up / had to fight off that temptation, and so I can recognize those categories, sometimes I can get frustrated with people who aren't even trying.