I do agree with you that "dignity" is pretty much subjective...
and as you said, yes - there are many 'jobs' which can compromise
one's dignity to a certain level. Even those that do not involve
the sale of one's body can also be 'undignified' in many
ways.
Having said that, I do question this: regardless of the reasons
that would make a person choose / get into this line of work, I
can't help but wonder - isn't there a better option for them? Does
the lure of easily obtained earnings tempt them so much so that
they are able to just view what they do in a 'detached' manner?
Would it be entirely out of the question for them to earn their
keep in the most menial way as compared to their current
choice?
I have never believed that a person has "no choice" when it comes
to matters and choices pertaining to their life. "No choice", the
way I see it, sounds more like: "This may not please many people,
but I think it's the most workable option for me".
In certain circles and societies, there are many levels to the
"common prostitute". There are those who only would answer a call
for a certain amount of money, and there are those who are
specially trained as 'entertainers'. As far as I understand it,
geishas are the glamourised versions of perhaps the ladies you may
meet at Club Kabuki or Orchard KTV... they entertain, drink with
you, sing along - and are trained to say the right things to the
right people. They are all performers in their own way... and
perhaps play mind games better than the suspicious wife. BUT - they
are not obliged to have sex with their clients. It is their call,
at the end of the day, much like the geishas of yore.
Isn't it also a slight nudge to their dignity - to have to
mollycoddle, tease and stroke the egos of men whom they barely
know? Perhaps to some, it may be better to have to do that, than to
be caught at the dishwashing area of some decrepit coffeeshop. It's
all really a matter of perspective.
I have yet to read the book - but I will most definitely get it
when I next visit a bookstore... but coincidentally, I have just
finished reading "In The Company of the Courtesan" by Sarah Dunant.
That was what sparked the thought for this topic... it made me
realize that the job scope, throughout the ages - remain very much
the same; but the attitude of society has evolved
somewhat. For example, it is considered a public secret and
perfectly natural for a high ranking official to visit the most
sought after courtesans in 15th Century Rome, and these are ladies
who aren't only able to satisfy their carnal desires; but also
women who are well versed enough to hold a conversation with them.
"Revered" may be a strong word, but an appropriate one, in this
context, I'd say... when the most well known ladies are visited by
the most powerful men, and envied by the common folk.
At the end of the day - no matter how we choose to view the
profession, there may be certain aspects that may elude us
somewhat.
Just like most everything else in life. 
