Depending on what the alleged purpose of the chemtrail spraying would be, spray released above 30,000 feet is likely to be highly unpredictably dispersed due to high-altitude winds.

How do aircraft accused of depositing "chemtrails" manage to pass inspection without the deception being discovered?

Assuming drugging the population is the purpose, the people behind the conspiracy would breathe the same air the population breathes, so any harm inflicted on the population would also be inflicted on those in charge of the conspiracy, unless they were made immune through vaccination.

just some skeptical questions i found about these things online