You don't want someone cutting or snipping a hair sample
from a candidate's head with a sharp instrument. Who
do you think they will sue if something bad happens ?
You don't want someone yanking a hair sample from a
candidate's scalp --- because of possible infection.
You don't want to gamble that all the environmental
compounds landing on the hair will be ignored, and
will not lead to false results.
You don't want to bet your defense on a technology that
is backed up by very little case law.
You don't want someone cutting or snipping a hair sample