Why is it not a good idea to use pure vegetable oil in a conventional diesel engine?

W) Straight vegetable oil will not work in a diesel engine

X) Straight vegetable oil produces more emissions than regular diesel

Y) Straight vegetable oil will damage the diesel engine over time

Z) Straight vegetable oil does not allow diesel engines to work at high speeds
Y) STRAIGHT VEGETABLE OIL WILL DAMAGE THE DIESEL ENGINE OVER TIME