The basic argument is extremely simple:
- AIs can, depending on context, pursue a task with complete disregard for humans/values
- In the future, AIs will have enormously more means and smarts
- An AI could then assess that humans are an impediment to its tasks, escape containment and proceed.
You really need to read the reports, you'll be surprised.
AI 2027 is an entertaining read. Its timeline is way too compressed IMO, but it's plausible.