It is interesting how widely the responses vary. Some say it's an uphill battle to scratch out a $40,000 income, while others say $80,000 is doable. It sounds like much of one's success depends on ability to develop a well-paying private clientele. Without that, you have to rely on the companies, which is possible but, because of the low rates, not at all fun. To find enough private clients, there are obvious factors that would work to one's advantage from a marketing perspective. Native-speaker English status and physical presence in a Western country would probably be big advantages.
a normal person writing term papers full time makes about as much as a teacher, ironically enough, but with no benefits and questionable job stability.
First of all, what do you mean by "develop the contracts you need to make it full time"? What essay writer has contracts?
I, like you, am in part-time mode. As for it being silly as a career ... well, on the one hand, I can't see a young person setting this as a lifetime career goal, it's true. On the other hand, if some writers are making 80k, and they like the work, then I can't knock it. Indeed, there are no benefits and you can't exactly advance. But that is the case for a lot of people nowadays, even if they might work in an office or other "real" setting. Stability is a concern, but in general, I would say the market for academic writers is strong and will be that way indefinitely. You're much safer if you have your own clients rather than relying too much on companies, though. Your real "stability" concern comes if you get sick and can't work. It's probably a small number of people who can pound out nothing but essays year after year, but I don't think it's exactly silly, especially if you love working at home.