What's a proper approach to use with those who literally can't handle that much truth?

Good question, though we might also want to take a careful look at whether there's something a little askew about the truth we're offering.

How can the folks who can't handle this stuff easily or perhaps at all be identified?

Rationality helps some depressed people and knocks others down farther.

Even if people at risk can be identified, I can't imagine a spoiler system which would keep all of them away from the material. On the other hand, maybe there are ways to warn off at least some people.