Poor families are far less likely to be able to afford legal counsel, let alone arrange for a sufficient amount of 'blood money' to pay to the family of the victim. Wealthy individuals/families are far more likely to be able to arrange sufficient amounts of 'blood money' to sway the families of victims. The law is therefore prejudiced against poor people.
In addition, allowing a victims family or victim to 'forgive' an individual who has committed a heinous crime is not in the interests of society. A murderer or rapist is still a threat to society (in terms of committing more murders or rapes) if he is allowed to go free just because the victim or victims family accepted money. The practice also creates an environment in which wealthy and influential individuals can coerce the victim or victims family to 'accept blood money' and 'forgive' the criminal. 'Blood money' in exchange for forgiveness is therefore an extremely flawed practice and/or law and should be repealed.
Piece by piece this edifice of bigotry, intolerance and hatred constructed in the name of 'Islam' in Pakistan by the Mullah Raj and their apologists shall be chipped away at until it stands no longer.