Earlier quoted context omitted.
It's been tested for years (decades? it's generic) as an anti-malaria drug. Any drug can be overdosed.
That's an oversimplification. The amount for an overdose is only around 3X a regular dose (2g vs 600mg) In contrast, most drugs for which you overdose need to be at much higher dosage multiples compared to the prescribed dose.
Perhaps for over the counter medication. This statement is false when we consider drugs requiring a prescription especially those used mainly in acute care or hospital situation. There are all sorts of medications in that class for which a double dose will straight up kill you.
In discussing such situations we often use terms like "patient safety" and "medical malpractice".
The arguments for against this drug seem center around the person recommending it, not its actual efficacy.