The lives of scabs should not be easy, nor should they expect them to be. They are close to the lowest form of humans in the western world.
I don't think they should suffer harm but harrassmemt is a fair ploy to be used. A person who won't support fellow union memembers who are on strike or will cross a picket line as a replacement worker is worse that the pus from an infected sore.
Verbal harassment is fine, free speech being what it is.
Harassment in the form of property damage or violence, which is what unions *always* use? No - or are you advocating such?
I used to be a Teamsters member. Then I wised up, left the union and got a better job elsewhere - without a union.
I can only assume that you are a union member. If so, it may behoove you to look into where your union dues are going. The answer should surprise you.