The unions are so adverserial because in the past capital sent literal paramilitaries to murder union members. See the crap the Pinkertons pulled. So many of the labor rights we have are because brave men and women were literally willing to risk their and their families' lives to speak out against management.

And it's not somehow magically different now; the woman responsible for the Panama Papers got car bombed and it was just swept under the rug. Capital is more than willing to use extralegal lethal force to protect itself, to this day.