I've been watching Firefly. While I've been enjoying the show, the one thing I haven't been able to quite figure out is why companions have such high social standing. They are admittedly quite "posh", but what about them makes them so well received among the upper class?
They're much more than just prostitutes.
From the Firefly Wikia:
Registered Companions are culturally well-educated with training in a number of areas, including psychology, music, fencing, and languages, as well as unarmed martial arts. On the "core" planets, Companions were typically trained from a very young age.
This is not unrealistic: compare with the real-life oiran, Japanese courtesans some of whom had fairly high status in society, doubtless much more than a bandit, smuggler, and 'petty thief' such as Malcolm Reynolds would have had:
Compared to yūjo (prostitutes), whose primary attraction was their sexual favors, courtesans were first and foremost entertainers. In order to become an oiran, a woman had to be educated in a range of skills, including the traditional arts of sadō (Japanese tea ceremony), ikebana (flower arranging), and calligraphy. Oiran also learned to play the koto, shakuhachi, tsuzumi (hand drum), and shamisen. Clients also expected them to be well-read and able to converse and write with wit and elegance.
Within the pleasure quarters, courtesans' prestige was based on their beauty, character, education, and artistic ability, rather than their birth.
The highest rank of courtesan was the tayū (太夫?), followed by the kōshi (格子?). Unlike a common prostitute, the tayū had sufficient prestige to refuse clients. Her high status also made a tayū extremely pricey—a tayū's fee for one evening was between one ryo and one ryo three bu, well beyond a laborer's monthly wage and comparable to a shop assistant's annual salary.
Given the similarities between the above description of oiran and some of what Inara tells us about Companions - even down to specifics such as the tea ceremony - it seems likely that Joss Whedon consciously based the Companion system on the real-life oiran. But I haven't yet found anything canonical to confirm this, so I've asked a question about it to find out.
While there is no doubt that companions are sex-workers they are much more than that.
From Wikipedia (re Inara)
... Companion, a high-society courtesan licensed by the Union of Allied Planets (the "Alliance").
In Alliance society, Companions are part of the social elite, often accompanying the wealthy and powerful. There is considerable ritual and ceremony surrounding their services, which appear to extend beyond sex to nurturing psychological, spiritual, physical, and emotional well being.
Companions do not view themselves as prostitutes and are insulted by the suggestion.
Companions choose their own customers, and to be chosen by one is considered a great honor and status symbol, as those chosen must be both wealthy enough to afford a Companion's often steep price and desirable enough to attract one
So, a companion is a highly skilled legal professional that has been through extensive training in the services they provide and, just like any other highly sought after professional, are welcomed accordingly.
Note also that they choose who they will have as clients, not the other way around. They imbue status on their clients making them highly prized.