It’s not so much a toxic culture as an unforgiving one.
I’ve often wondered myself where such vitriol comes from sometimes.
It's probably been discussed several times before and I may be way off base, but the reviews and feedback here come from punters investing their own hard earnt cash. Quite often it involves an element of risk, e.g. when you enter a brothel for the first time or see someone who has no feedback. The hard time that newbies get while they establish their credentials helps ensure that anything they say is credible and trustworthy. Trust is an important currency here. Punters who share their honest experiences help other punters to lower the risk of wasting their own money, getting ripped off, or getting a crap service.
This lower risk is a real and valuable benefit. It's what distinguishes UKP from any other punting forum. In business, this benefit of lower risk would be chargeable. However, on UKP, it's free. The way people can "pay" for this benefit is by contributing themselves. It's not a law, it's not written down, but nominally it's the way it works. It's old school trading.
People who don't contribute are taking advantage of the risks (money spent) that other punters have taken. This rankles and fuels the behaviours and reactions against them.
Supposedly UKP is the Tripadvisor of escorts but, in reality, it's not. Tripadvisor has loads of fake and paid-for reviews and makes it money from travel companies (equivalent of SPs) advertising. UKP is not like that. It isn't revenue generating and members fight really hard to maintain the integrity of the reviews. Look at the way touts and white knights are treated. Long may it continue.