I don't think that commodifying sex is worse or different than commodification of teaching and of taking care of children, for instance. More generally speaking, in what way is it different from commodification of making goods and of offering other kinds of services, for that matter? I don't agree that sex work is 'the ultimate commodification of human activity' as you put it. It is _the way you view sex_ that makes you think that the word 'whore' is 'a potent metaphor for selling out.'
There are many jobs that involve becoming naked--for instance, acting, modeling, etc.
Vulnerability of sex workers doesn't come from the commodification of sex per se. It comes from illegality, moral condemnation, social ostracism, economic conditions, sexism, etc.--material and ideological conditions of work.
Yoshie