Could you please elaborate on what Islam has to say about a person or persons who wrongfully blame a person of wrongdoing or an immoral act?
Obviously no sane person would say that such an act should be condoned. Islam however, prescribes punishment for some of the serious allegations that are labelled against someone falsely to harm his repute. Take for example the matter of Qazaf. Qazaf is to slander someone of having extra marital sexual relationship. If it is proved that someone has falsely accused a person of repute he must be punished. The holy Qur'an says:
وَالَّذِينَ يَرْمُونَ الْمُحْصَنَاتِ ثُمَّ لَمْ يَأْتُوا بِأَرْبَعَةِ شُهَدَاءَ فَاجْلِدُوهُمْ ثَمَانِينَ جَلْدَةًوَلَاتَقْبَلُوا لَهُمْ شَهَادَةً أَبَدًا وَأُوْلَئِكَ هُمْ الْفَاسِقُونَ إِلَّا الَّذِينَ تَابُوا مِنْ بَعْدِ ذَلِكَ وَأَصْلَحُوا فَإِنَّ اللَّهَ غَفُورٌ رَحِيمٌ وَالَّذِينَ يَرْمُونَ أَزْوَاجَهُمْ وَلَمْ يَكُنْ لَهُمْ شُهَدَاءُإِلَّاأَنفُسُهُمْ فَشَهَادَةُ أَحَدِهِمْ أَرْبَعُ شَهَادَاتٍ بِاللَّهِ إِنَّهُ لَمِنْ الصَّادِقِينَ وَالْخَامِسَةُ أَنَّ لَعْنَةَ اللَّهِ عَلَيْهِ إِنْ كَانَ مِنْ الْكَاذِبِينَ وَيَدْرَأُ عَنْهَا الْعَذَابَ أَنْ تَشْهَدَ أَرْبَعَ شَهَادَاتٍ بِاللَّهِ إِنَّهُ لَمِنْ الْكَاذِبِينَ وَالْخَامِسَةَ أَنَّ غَضَبَ اللَّهِ عَلَيْهَا إِنْ كَانَ مِنْ الصَّادِقِينَ(24 :4-9)
Those who accuse honourable women and bring not four witnesses as an evidence [for their accusation], inflict eighty stripes upon them, and never accept their testimony in future. They indeed are transgressors. But those who repent and mend their ways, Allah is Ever-Forgiving and Most-Merciful. And those who accuse their wives but have no witnesses except themselves shall swear four times by Allah that they are telling the truth and the fifth time that the curse of Allah be on them if they are lying. But this shall avert the punishment from the wife if she swears four times by Allah and says that this person is a liar and the fifth time she says that the curse of Allah be on her if he is telling the truth. (24:4-9)