I think rexknobus is right. And I think this scene where Harmonica tears up Jill clothes is not meant for those Frank's gangsters. It is a show for us. Leone took a common clishe and turned it upside down. Tough unknown stranger is attacking beautiful widow, he is trying to rape her. Or does he? Sergio wanted to ruin our expectacions, and he suceeded entirely. If he doesn't want her body, then what does he want? Result: his actions are very odd to us, wich adds to the aureol of mystery around Harmonica's character. Also, this scene prepared us for future events in this movie. He is not after quick pleasure, that is what we can conclude from this scene; he is not after money either, we can see it from the auction scene and after when he returned "his farm" back to Jill.
...Jill arrives in McBain's Sweetwater . . . wearing the fine clothes . . . that apparently her profession has enabled her to afford. Then Harmonica literally recuts her dress by tearing off the long sleeves and lace in a series of gestures that look like rape but turn out to be his attempt to mold her into some kind of superpeasant, whose now partially exposed breasts suggest her maternal relation to the new social order that is struggling to be born out of the masculine desert. (182, 183)
Harmonica cannot be killed because in some sense he is already dead. But, for the same reason, he is not really capable of love and the communal social identity that love makes possible. Yet he fosters such a community in his attempt to shape Jill into the kind of revolutionary subject he cannot be. After he recuts her fancy dress in the scene that resembles a rape, he tells her to fetch him some water from the well because he likes his water fresh. Though this request is actually a stratagem that enables him to gun down the men Frank has sent to kill Jill, it also articulates symbolically his relation to Jill, since he is part of death's landscape that only Jill's water can revive. Even Frank recognizes a tremendous life force in Jill that makes him regret having to kill her. In this respect, Frank, Cheyenne, and Harmonica share the same death drive that finds its only possible reversal in Jill's vitality, which takes the form of sexual pleasure for Frank, coffee for Cheyenne, and water for Harmonica. (185)