Why have unbelievers cast aspersions on all prophets throughout history?

The fact that prophets always communicate the religion of Allah never pleases unbelievers. This is because people who understand and fulfil what they are told demonstrate a change in themselves and move away from the superstitious systems of the unbelievers. For instance, since they know that they should fear only Allah after they become believers, it is no longer possible to frighten them with any other thing. Since they always consider the benefits of the religion in every action they take, it becomes very difficult to intimidate them or lead them astray. These people, no matter what the conditions are and no matter what they are offered in return, do not hesitate to say what is right and just, and do not diverge from what they believe to be right.

This annoys unbelievers, because it endangers their personal worldly interests. For instance, whereas unbelievers try to live and make others live according to their own ideas, believers who adhere to the example of the prophet follow only the commands of Allah. They teach people the inappropriateness of the ignorant system that unbelievers live in, and the beauty of the religion which will bring peace and happiness to people both in this world and in the Hereafter.

For these reasons, in every age, unbelievers have attempted to hinder messengers by using various methods. Examples of this are related in the Qur’an. By means of inconsistent and irrational arguments, unbelievers attempt to deny what Allah’s messengers convey. They try to stop them with verbal threats. When verbal means fail, they try to make believers revert from the right way by means of real physical methods. However none of these methods works; they can never bring forth convincing evidence against the truths that messengers and sincere believers convey; nor can they put forward ideas that successfully oppose ideas based upon truth.

In many verses Allah has given examples of the verbal assaults of unbelievers, and of groundless allegations they made against prophets:

The ruling circle of those of his [Nuh's] people who disbelieved said, “This is nothing but a human being like yourselves who simply wants to gain ascendancy over you. If Allah had wanted He would have sent angels down. We never heard of anything like this among our ancestors, the earlier peoples. He is nothing but a man possessed so wait a while and see what happens to him.”  (Surat al-Muminun, 24-25)

What is he [i.e., Nuh] but a man who has invented a lie against Allah? We do not believe in him. (Surat al-Muminun, 38)

… But they said [for Musa], “A lying magician.”  (Surah Ghafir, 24)

Allah relates in one verse that such aspersions have almost been a tradition among unbelievers:

Equally, no Messenger came to those before them without their saying, “A magician or a madman!” Did they bequeathe this to each other? Indeed they are an unbridled people.  (Surat adh-Dhariyat, 52-53)

Why have unbelievers cast aspersions on all prophets throughout history?