I guess you can call it a cult, but it's very mainstream and popular. I don't really find any way to draw a line between "cult" and "mainstream religion." Baptists and other conservative Evangelicals vociferously dispute the notion that they are cultists. Given that they're one of the largest, if not the very largest, organized group(s) of Christians in the United States, it's pretty hard to dispute their dispute, as it were.

I guess it depends on how you define "cult."