Lyric discussion by dgfthqy 

Cover art for No More lyrics by Elliott Smith

i interpret this as him saying his depression is kind of a lie, even though it's not- i do this to myself to where i'll criticize myself for being depressed and feel it's just a thing i do to cast blame, and remain paralyzed so i don't have to function- so i can stay helpless.

"arguing his case" is all the negative thinking where he might feel he's trying to convince himself he has a reason to feel so mentally incapacitated, all the while feeling himself a farce.

He also, in my interpretation, is saying that his depression is a "useful dream" in that it allows him to be useless- it lowers one's expectations of oneself because you can blame everything on the depression instead of dealing with your situation proactively.

it isn't logical thinking, but i partake in it, and i think this is what he means.

this thinking is replicated in King's Crossing where he refers to himself as a "method actor".