I think there's another step missing between being convinced that AI will replace human labor and that AI is the most pressing x-risk (which is the starting point for the article you linked), but this gives me an idea of what the form of your answer would be:
Not only will AI replace human labor, it's also extremely dangerous (for reasons laid out elsewhere on LessWrong / MIRI / various lukeprog-created websites :)), so we really need to solve the more general problem of AI x-risk.
Kevin Drum has an article in Mother Jones about AI and Moore's Law:
Although he only mentions consumer goods, Drum presumably means that scarcity will end for services and consumer goods. If scarcity only ended for consumer goods, people would still have to work (most jobs are currently in the services economy).
Drum explains that our linear-thinking brains don't intuitively grasp exponential systems like Moore's law.
He also includes this nice animated .gif which illustrates the principle very clearly.
Drum continues by talking about possible economic ramifications.
Drum says the share of (US) national income going to workers was stable until about a decade ago. I think the graph he links to shows the worker's share has been declining since approximately the late 1960s/early 1970s. This is about the time US immigration levels started increasing (which raises returns to capital and lowers native worker wages).
The rest of Drum's piece isn't terribly interesting, but it is good to see mainstream pundits talking about these topics.