Somewhat unexpectedly, the previous post on Latin conventions in Spartacus has garnered quite a readership. Vox Populi, I guess. Poking around the web has uncovered some other criticisms of the show that might be relevant.
There are those that object to some of the vulgarities. One commenter elsewhere suggested that words like f***, s***, and c*** were inappropriate for characters who, on the other side of the translation convention, should be speaking Latin. It's true, those particular words have Germanic roots, but it's not like classical spoken Latin would have been entirely without local equivalents. A long enough immersion in colloquial Italian would uncover a range of colorful invective, metaphorical imagery, interjections and curses. There's no reason to expect that the language of classical-period Capua would lack such things. We don't find a lot of evidence for it in the extant Latin literature, but those works were written in a deliberate formal style for an upper-class audience. The invective of the streets would naturally be filtered out.
There is further criticism of the show, in that some of the characters speak in accents. This is the result of a long standing trope (known to tv.tropes.org as The Queen's Latin). We as viewers are accustomed to upper-class Romans speaking English in RP. Meanwhile, the lower class slaves speak in a motley assortment of accents, reinforcing the concept that they come from many places within and without the Republic. That the cast is multinational only helps reinforce this convention.
The characters portrayed in the series are not (with a few exceptions) Roman aristocracy. All of the gladiators we see are slaves. They carry infamia. They are non-persons, and standard Roman dignities would not apply to them. Further, they live communally in an all-male, testosterone-fueled environment. Modern concepts of privacy and modesty don't apply to them. They would, by necessity, become accustomed to bathing, eating, sleeping, and performing other activities in each others presence. It is almost inconceivable that they would watch their language. A modern equivelant is to look at modern soldiers, sailors, or marines living with one another in the field. To 'swear like a sailor' is already a truisim in our culture.
Despite the infamia, these gladiators are also celebrities (this is one of the contradictions of the gladitorial games). It's sometimes helpful to think of them as some combination of modern professional wrestlers, professional athletes, and rock stars. Extant graffiti uncovered in Pompeii reveals adulation of popular gladiators, much of it quite vulgar. Reinforcing the image was the popular perception of gladiators as "beasts in human form", full of barely suppressed fury and violence. The Freudian and Jungian associations between violence, gore, and sex should be obvious to most modern viewers. The blatant sexual displays seen at the gladiatorial games is unlikely to be out of place. Many modern stadium rock stars experience similar skin exposure, and some revel in 'groupies' attempting to take advantage of their reputations for sexual prowess.
Beyond that, this is a protrayal of pre-Christian Greco-Roman culture. One could realistically expect more open portrayal of sex and sexual characteristics. While one would not expect naked sexual behavior to be openly desplayed, there is little cultural repression of sex and sexuality in Roman culture. Fecundity, fertility, and virility are celebrated traits, to the point where sculpture openly displays such attributes.
The behavior of Batiatus and his wife is a little more unexpected, but not entirely out of place. Batiatus is portrayed as a middle-class Roman, pater familia of a gladiatorial ludus, but with social ambitions. His profession is not illegal, but isn't considered quite in keeping with the propriety of an aristocrat. His position might be roughly equivelant to a modern owner of a football team or gentleman's club. Further, he's removed from the political and cultural center at Rome. Thus, it's not entirely unquestionable that he would use his property (villa, slaves, and gladiators) as a mechanism to secure favor and patronage. Being removed from Rome allows visiting aristocrats to engage in licentious behaviors without the reprobation or negative reputation they might gain from public exposure. They thus preserve a veneer of respectability, and Batiatus hopes to gain from protecting it.
The language and behavior thus shown in Spartacus is not entirely out of the question, and such criticisms levelled against the show are not entirely merited. While there is not a concrete historical record in support of the things the creators have chosen to show us, such tropes are not entirely unlikely.