What credentials beyond "thinking about this problem a lot" would satisfy you? He works at his own research institute dedicated to this topic, wrote some books on it and other (self proclaimed) alignment experts take him seriously.
I mean, his whole thing is "progress on AI research leads to the apocalypse." He's done some work on decision theory, but they're not connected to DL, presumably because he thought "well if DL works out in the short term we're all dead anyways." Which seems to be what's happening.
