Why are scientists concerned about the use of the Bt toxin which is used to kill insects in genetic engineering

The toxin Bt (endotoxin CrylA (b)) Bacillus thuringiensis that is a normal inhabitant of the soil, showed himself as a natural insecticide used by farmers engaged in organic farming. In contrast to the Bt-toxin produced by bacteria, genetic engineers included it pesticide in every cell of the seed, and therefore distributed throughout the adult plant, the products from which then are consumed by man. That's why scientists are concerned that after the use of a BT toxin products people get antibiotic resistance and resistance to bt.