The word cult can be defined in many ways. I usually define it as having strange beliefs or practices. Consider a short list of JW beliefs and practices and see what you think:
They sacrifice humans and their children due to the flawed blood doctrine
They shun people because of thought-crimes
The wickedly shun children who have the misfortune of getting baptized at a young age and then disfellowshipped at a young age - for many such ones they never get reinstated so their disfellowshipping turns into a life sentance. I personally know of several young ones DFed at ages between 13 and 18 who are serving a life time of shunning
They speak out against education
They do not get involved in making the community better
They do not help clean up the environment