The job pays too little based on the fact that it can leave the "employees" traumatized and scarred for life.
But it does not take away from the fact that it can negatively affect the employees in an adverse way long term, and takes advantage of poor people to give them an objectively bad deal based on an information asymmetry where the person in question might not know that they have to read graphic descriptions of bestiality and pedophilia.
This is an argument that the job shouldn't exist at all. That's an okay argument to make (I personally lean that way), but has no relevance to whether $2/hour would be worth it to a Kenyan.
I think people can make that choice as long as it's informed. The company should also be providing mental health support as part of the job. Someone has to do it. There aren't automated systems that can do a remotely decent job at moderation yet. I know you don't think it's okay for trained systems or social networks to distribute traumatizing material.
Scarred for life by reading/labeling text?
There is obviously a big difference between labelling pictures or video and text. I would be open to seeing an actually study, but my prior would be that text must be harmless. I would certainly be open to reading any text, especially if the context is that the text is for training purposes.
But it does not take away from the fact that it can negatively affect the employees in an adverse way long term, and takes advantage of poor people to give them an objectively bad deal based on an information asymmetry where the person in question might not know that they have to read graphic descriptions of bestiality and pedophilia.