Benedick makes a very sexist speech, but he is not really as bad as he seems. He is just in love.
Benedick is in love with Beatrice (and she with him), but neither will admit it. He likes to play tough, making comments about how marriage is terrible and not for him.
That a woman conceived me, I thank her; that she
brought me up, I likewise give her most humble
thanks: but that I will have a recheat winded in my
forehead, or hang my bugle in an invisible baldrick,
all women shall pardon me. (Act 1, Scene 1)
Benedick sees Claudio, in love with Hero. He wants to disparage Claudio and the whole enterprise of pairing up. After all, according to Benedick, being in love just makes a man grumpy and all lovers are fools.
I do much wonder that one man, seeing how much
another man is a fool when he dedicates his
behaviors to love, will, after he hath laughed at
such shallow follies in others, become the argument
of his own scorn by failing in love: and such a man
is Claudio. (Act 2, Scene 3)
Benedick swears that he will not be a fool, and makes a silly list of the traits of his ideal woman. She needs to be rich, wise, and virtuous. She also has to be a conversationalist and play a musical instrument. He creates a perfect, unattainable woman.
It is easy to dismiss Benedick as a pig. However, his words are just a cover how he really feels. Benedick is not exactly a playboy. He has been hurt. He was in love with Beatrice before, but she, like him, has sworn off of love. Both of them are playing tough to cover for the fact that they are really interested in each other.
However, when Benedick is tricked into revealing his true feelings, it is different. Benedick thinks that Beatrice loves him, and he begins to express his real view of love. He may play a shallow playboy, but in reality Benedick wants the same things we all want. He wants someone to be with.