Tacitus on Mythicism

Although I can empathize with mythicists’ avoidance and/or skepticism of Josephus as evidence for a historical Jesus, given the clear evidence for tampering, I do not understand why anyone who had not already set out in advance to disprove the existence of Jesus would doubt the testimony of Tacitus (Annals 15.44) writing in the early second century:

Such indeed were the precautions of human wisdom. The next thing was to seek means of propitiating the gods, and recourse was had to the Sibylline books, by the direction of which prayers were offered to Vulcanus, Ceres, and Proserpina. Juno, too, was entreated by the matrons, first, in the Capitol, then on the nearest part of the coast, whence water was procured to sprinkle the fane and image of the goddess. And there were sacred banquets and nightly vigils celebrated by married women. But all human efforts, all the lavish gifts of the emperor, and the propitiations of the gods, did not banish the sinister belief that the conflagration was the result of an order.

Consequently, to get rid of the report, Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace. Christus, from whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of one of our procurators, Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judaea, the first source of the evil, but even in Rome, where all things hideous and shameful from every part of the world find their centre and become popular. Accordingly, an arrest was first made of all who pleaded guilty; then, upon their information, an immense multitude was convicted, not so much of the crime of firing the city, as of hatred against mankind. Mockery of every sort was added to their deaths. Covered with the skins of beasts, they were torn by dogs and perished, or were nailed to crosses, or were doomed to the flames and burnt, to serve as a nightly illumination, when daylight had expired. Nero offered his gardens for the spectacle, and was exhibiting a show in the circus, while he mingled with the people in the dress of a charioteer or stood aloft on a car. Hence, even for criminals who deserved extreme and exemplary punishment, there arose a feeling of compassion; for it was not, as it seemed, for the public good, but to glut one man’s cruelty, that they were being destroyed.

Why would a Christian invent such a negative report, if it was a forgery? And if it is authentic, but some would claim that Tacitus was dependent on the Gospels, we must ask why would someone who viewed Christians as criminals supposedly trust information from them or sources belonging to them? Once again, almost anything is possible, but is there any justification for the mythicist viewpoint (which may not be held by all mythicists, I readily acknowledge) that this information more likely to be unreliable than reliable?