This brings up an interesting question: What's the difference between a religion and a cult? Well to answer such a question, there would need to be a definition of religion given first. If you use my definition of religion (the belief in and worship of at least one deity) then the difference between a cult and a religion would be that in a cult the person, idea or object worshiped is not thought of as a deity but is still highly revered. So for example, if a charismatic person was worshiped but not believed to be a deity by their followers, then that would be a cult. If however, the followers thought of that person as a deity, somehow endowed with supernatural powers, then it is a religion.
Dictionary.com offers us some definitions of a cult:
1. a particular system of religious worship, especially with reference to its rites and ceremonies.
2. an instance of great veneration of a person, ideal, or thing, especially as manifested by a body of admirers: the physical fitness cult.
3. the object of such devotion.
4. a group or sect bound together by veneration of the same thing, person, ideal, etc.
5. Sociology - a group having a sacred ideology and a set of rites centering around their sacred symbols.
Under all of these definitions, all religions would be cults. That's why I differentiate them with the existence of perceived divinity. The definition of a deity is also important. The cargo cults of the South Pacific worship airplanes because they think they are sent by their dead ancestors and are somehow magical or divine. That would technically make them a religion under my definition, but depending on how you define a deity, other may disagree.
The problem with demarcating the difference between a religion and cult is obvious. There are no agreed upon definitions of either of them, and depending on how you define them, they can all kind of blend into one another, making it very hard, if near impossible, to discern one from the other. That's why I think it is a good idea to challenge any theist you find yourself debating with, to ask them what the difference between a cult and a religion is, just to see what definitions they give you. You might be able to make them admit that their religion is a cult under their own definition - something they will want to deny but a trap they will have made for themselves.