Please provide sources around the idea of "enduring" pain. Zen, and Buddhism in general, focuses a lot around compassion.
People can encounter quite a bit of pain from sitting but the advice is to relax and "let go" of the suffering as much as possible rather than "soldier on".
These are not dangers of meditation in itself, but issues on how it is taught and understood.
Some forms of meditation can be inherently risky for people facing mental illness or emotional distress. That's why a good teacher is needed.
> idea that the practice teaches you to be able to handle enormous stress.
I never heard this in a Zen setting.
> Practioners are taught to stay in meditation through physical distress, through mental distress, even while being hit with sticks, etc. This is a form of training.
Phrased like this it sounds like Full Metal Jacket.
Zen, and meditation in general, can push people into confronting their emotions and inpulses and can be challenging, like psychotherapy. But it's not an ascetic practice and the endurance of suffering is not its goal.
People can encounter quite a bit of pain from sitting but the advice is to relax and "let go" of the suffering as much as possible rather than "soldier on".