Not sure what kind of "argument" the poster is expecting, but I consider it fairly obvious that an entity that 1. is as far superior to humans as humans are to ants (pick your favorite alternative analogy), and 2. does not share any evolutionary or social commonality with humans is both extremely dangerous and extremely unpredictable. While I'm not completely convinced by the "AGI = annihilation" idea that LessWrong…
An argument that makes all of its relevant assumptions clear and using precise distinctions would move "fairly obvious" and "seems to be so sure" and "sounds naive" into crisp statements about our knowledge. That's why it's desirable. Its use goes beyond simply you being convinced.
If "a being that you don't understand and that is better than you at everything is a potential danger to you" doesn't convince someone, I'm not sure what further elaboration could achieve. This is a classic problem that arises in many philosophical debates. If there is disagreement about fundamentals, the debate doesn't (and can't) go anywhere.
The real problem is that we simply cannot hope to predict what an entity that is far superior to any human would do, essentially by definition. So I wouldn't frame this as a "debate" so much as two camps of different beliefs. Any "argument" made is like ants trying to understand human ethics. While I consider the aforementioned point to be obvious, I could be wrong about it in ways I can't even comprehend, and so could any other human, regardless of their degree of expertise.
Ironically, this unknown provides something like a meta-argument for extreme caution when dealing with AGI: Just like you wouldn't step blindly into a dark room that might contain a monster, you don't have to know that AGI is dangerous in order to be afraid of it – the mere fact that it might be and you cannot ever know for sure is enough.