At the time when Petronius wrote The Satyricon, the population of freedmen in Rome was relatively large, even more so in the Italian peninsula as a whole. They were given the same level of citizenship as free-born Romans but were seldom accepted as equals, being widely considered as vulgar parvenus who had acquired manumission by good luck. As such, their social status as freedmen was seen as really no different from that of slaves in that both groups were ultimately dependent upon the whims of masters.
There was an additional reason for the general contempt of society towards freedmen. Roman society traditionally derived its wealth and stability from agriculture. Despite the notable expansion of trade and commerce, the ownership of land, especially farmland, still enjoyed an elevated social status in the eyes of most Romans, particularly among the aristocracy. Freedmen, however, being less class-conscious, had no compunction in getting their hands dirty, making as much money as they could in the vulgar world of trade and business.
Trimalchio is the epitome of the nouveau riche freedman whose dazzling wealth acts as a standing insult to the Roman upper classes. He is unapologetically brash, throwing lavish parties and adorning the walls of his house with vulgar paintings depicting himself and his journey from slave to wealthy arriviste.
Yet Petronius is much too good of a writer, much too subtle in his biting description of Roman society in all its hypocrisy, to engage in one-dimensional snobbery. His characterization of Trimalchio, and by extension of freedmen in general, is a good deal more ambiguous than we might expect. Trimalchio has bought his way into the upper echelons of Roman society, though without being fully accepted. Nevertheless, he still imbibes the general air of decadence breathed greedily by the Roman elite, so there is a rude kind of equality at work.
There is a difference, though, between Trimalchio and his noble acquaintances and dinner guests. And this difference is crucial for an understanding of the portrayal of freedmen in The Satyricon. Trimalchio is who he is, unabashedly so. He doesn't pretend to be anything other than a freedman, albeit an enormously wealthy one who loves to flaunt his riches at every available opportunity. But this makes him considerably more honest, and more recognizably human, than the old money nobility who hypocritically wax lyrical about the virtue of the simple life of the Roman noble while at the same time throwing themselves into a pit of utter debauchery at the drop of a hat.