Short : Why sandboxing doesn't work.
tl;dr : this and this, but especially this and this.

I'll even give you a detailed account of the different steps I went through, I'm all too happy to answer. 

Unexpected sidenote : Anticipating as many counter-arguments as you can seems to me to be a very good strategy during a presentation. In my local EA student group, I made sure to cover 9-10 common counter-arguments, and the results were quite impressive (one person pivoted from unconvinced to quite convinced). 

So here is how it evolved for me :
1-Superintelligence risk is a topic + jpeg inventor says singularity is possible during a conference at uni.
Me : Ok, but its sounds just crazy, and I feel bad hearing about it. They all must be crazy. Or I must exagerate the problem in my head. Let's forget about it.

2-Defining instrumental convergence, and reframing AGI as an algorithm, and not a robot apocalypse.
Me : Ah, I see why it'd be a problem. But it'll figure out ethics on its own, right ?

3-Orthogonality thesis
Me : Oh, I see the problem now. Well, let's just sandbox it ?

4-Containment problem
This one took me a while. You really need to exhaustify as clearly as possible the different scenarios and models. The first time it was explained to me, some of it was left implicit, and I didn't understand. I almost felt like I was "harrassing" the presenter to get it finally spelled out, and that caused a big update in my head.
Me : Oh, ok, damn. But it seems very theoretical, or I don't know, socio-historically situated. It sounds like a sci-fi thing.

5-Seeing the expert surveys, and that people like Stuart Russell and not only people like Elon Musk are worried about this.
Me :  Ok, but that still seems very, very far away.

6-Discovering AIs that are scary as shit and yet not powerful.

I would definitely rank 4 (containment) as the most crucial one. Weren't it for my "harassment", I think I would have went past the entire cause area.
A fellow in our group noted 5 (expert surveys) as being the most convincing. 
The only argument I dared to publicly share on social media however is 6 (existing AIs) -less related, but pretty robust.

PS : First written thing on the forum, sorry if I'm not respecting all the norms '^^