Your chemistry teacher isn't necessarily wrong.
One choice Mustachians must make is the standard of living they can afford by retiring early.
A retirement stash of $1M means an income of $40K assuming a 4% withdrawal rate. Your chemistry teacher might be assuming something higher than that, in which case your chemistry teacher was right under his set of assumptions. He might also be considering a wife and kids, that increases costs considerably.
I also think that people on this site tend to underestimate the potential risk for (1) high healthcare costs, and (2) future increases in taxes to cover governmental costs.
My workplace shells out considerable money for my healthcare, and it doesn't even factor into account that it will be more expensive to insure me as I get nearer to retirement.
There are a lot of factors that will affect retirement calculations, so to consolidate the retirement decision into a single number brings with it a number of unspoken assumptions.