Why do women get the credit always ?

I just dont understand that part. Why is woman the innocent and harmless and non-guilty side of all stories ? Can a woman not be cruel and criminal ? I just dont understand..Infact, many a times women are the crappiest and cruelest human beings one can see. If there is a break up the blame always goes to the man. Why is that so ? Can man be the only one having an affair and cheating on the girl ? What kind of fairness is this???

Women can also be so self centered and selfish. I am not trying to do some gender bias here and am not a feminist at all (you should have got it by now !). Are women really the weaker and the innocent side ? Naaahhh...Not at all :|