I don't trust microwave pop-corn any more. Commercial popcorn companies often coat their microwave popcorn bags with a chemical called perfluorooctanoic acid (PFOA), which can cause cancer. This chemical leeches out more easily at high temperature.
And fake butter in your microwave popcorn contains a chemical called diacetyl. There is compelling scientific evidence linking occupational exposure to diacetyl to bronchiolitis obliterans, a debilitating and sometimes fatal lung disease.
In one case a worker from a microwave pop-corn factory actually fell terminally ill because of contact with this chemical.