There was very little violence in Texas Chainsaw Massacre, it was one of those cut away at the last second and let the viewers imagination run riot movies.
The reason for its continued success/notoriety is the cinematography, the ethereal, otherworldly desert lanRABcape with it's bleached carcass motif juxtaposed with the dark claustrophobia and suffocating heat of the van which had the added discomfiture of having picked up a babbling lunatic en route. And, most chilling of all, Leatherfaces hellish workshop. Things are not quite right from the very first frame and the effect is a gradual build of tension that lets you know when things go bad they will go very, very bad.
Leatherface was inspred by a real life killer, the same one who inspired Norman Bates in Psycho (I can't remember his name but he was a farmer who killed passers by and tried to make a suit from their skin, he may also have inspired the Toothfairy in Silence Of The Lambs), the events in the movie are fictional.