Why is the word infidel in the koran i do not believe it was out there by allah.?

mohammed says of infidels, ' ' do not trust them, not associate with them, kill them where you find them '' infidel is used as derogatory word. it ostrecizes those who do not join islam. do muslims in u/s feel there neighbores who do not embrace islam are infidels? is this an evil word? islam seems to go one foot forward and two feet back using this type of languge.