I don't have anything against OF or sex work, but I've always though that negative judgements against clients suggest a negative judgement against the service provider. If the act of providing the service is OK then surely the act of receiving the service is also morally sound? Unless the service provider has a morally ambivalent attitude to their own work? I say this as someone who had a long term partner doing sex work. Contempt for clients seems unfair and possibly hypocritical. Just people trying to satisfy a biological and emotional need.
I don't think you can generalise white collar jobs that way. I've done both, and writing software all day takes way more out of me than when I did manual labour. But some white collar jobs don't require much effort at all. I wish it was easier to balance using your brain and your body for work.