In Much Ado About Nothing by Shakespeare, how are women so easily 'turned against'?

Claudio and Leonato turn against Hero, even with little proof that she has done something wrong. 

Hero’s fiance and father both turned against her, and no one but Beatrice came to her defense.  At their wedding, Claudio renounced Hero, saying that she had been unfaithful.  This was based on his seeing a woman he thought was her with another man.  Don John set him up.  He set them both up. 

Don John had nothing against Hero, or Claudio for that matter.  He just wanted to cause disruption on his brother’s estate.  He certainly accomplished that.  Hero was baffled when he accused her. She had done nothing wrong, because what Don John showed him was Margaret, not Hero, with Borachio, Don John’s accomplice. 

Claudio waits until the wedding to reject Hero, thereby ensuring that her reputation was ruined.  Hero is so distraught that she faints.  Beatrice says she is dead, and Leonato says she is better off that way. 

LEONATO

O Fate! take not away thy heavy hand.
Death is the fairest cover for her shame
That may be wish'd for. (Act 4, Scene 1) 

Claudio does not really have to explain himself, and there are no real attempts to allow Hero to clear her name.  She is obviously very upset.  Everyone just assumes that what Claudio says is true, and that is that. 

Benedick is the only man who really questions what is going on, and Beatrice tries to tell everyone that it isn’t true. 

BENEDICK

Sir, sir, be patient.
For my part, I am so attired in wonder,
I know not what to say.

BEATRICE

O, on my soul, my cousin is belied! (Act 4, Scene 1) 

Still, Hero is dead as far as the world is concerned, because that is the only way to save her reputation. What is worse, Claudio is offered and agrees to a marriage to a “niece” of Leonato’s, really Hero (but Claudio does not know that). This is so that Hero can remain dead, and Claudio can save face.  It is ridiculous that one woman can be so easily switched out with another.