Any organization, group, sect, etc. that seeks to control its members by threats of excommunication if the sect's rules are not followed is a cult. If it were easy to leave the FLDS, then it would not qualify as a cult. Basically, many other religions could easily qualify as cult-like as well.
The Fundamentalist Church of Later Day Saints is basically a cult. It wants to segregate its members away from the rest of the world. It also does not want the glaring eye of public on their polygamist practices. Those practices are fundamentally abusive towards women and girls. One should not that this opinion is not against Mormons in general.
Of course at first glance you could call this religion a cult, however at one point could not all Christianity and Judaism be called that. I will admit bad things happen in it and occasionally illegal things but to say that makes it a cult is a stretch since most of the truly odd things they do weren't around until warren jeffs like the banning of wearing the color red. But more to the point the usa was founded on the principal of freedom of religion. Besides what they do is normal somewhere else so to condemn them here would be wrong.
No, the FLDS is not a cult, any more than any other religion is a cult. People who do not know about or understand FLDS might think that it is a cult, but that is just religious intolerance. The people of the FLDS are kind. No one is forced to be in the FLDS. They are there by choice.