As the drive for growth and profit intrudes into all relationships, it captures even the bodies that exist to hold capital to account. Agencies of the state, newspapers and broadcasters, campaign groups and charities that claim to restrain corporate power fall under its spell. As their mission becomes confused and their purpose dissipates, substance is replaced with spectacle.

Fifty years ago, in his book The Society of the Spectacle, the French philosopher Guy Debord argued that “the spectacle” (the domination of social relationships by images) is used to justify the “dictatorship of modern economic production”. It both disguises and supplants the realities of capitalism, changing our perceptions until we become “consumers of illusion”. Here is an example of how it happens.

Last week, the Royal Society for the Prevention of Cruelty to Animals (RSPCA) issued a press release about the “incredible story” of Marina, a seal it rescued, that had become trapped under a rock on a beach in south Wales. “Moving a three-tonne boulder presents numerous challenges, but we were able to work with partners to free this seal, before giving her the six months of rehabilitation she so urgently needed.” Marina’s rescue is “testimony to the RSPCA’s tireless commitment to wild animals, and their welfare”.

On the same day, the RSPCA’s head of campaigns, pushed into a corner during an online argument, wrote this: “Seal shooting is not culling it’s about humane pest control.” He was defending the slaughter of seals by Scottish salmon farms.

The contradiction is at first sight incomprehensible. But the organisation has another role alongside rescuing animals such as Marina, which is to assess livestock farms, and award those that meet its standards its RSPCA Assured label. This mark of approval ensures that “you can feel good about your choice when shopping and eating out”. Of the 280m animals whose production and slaughter it approves every year, salmon account for 200m. It accredits 63% of Scottish salmon farms.

The RSPCA won’t publish a list of the farms it has approved, citing a “contractual clause in the membership agreement”. But of the 24 people who sit on the advisory group for its assurance scheme (according to the most recent published list), 20 work for salmon farming companies. These companies include the four named in an investigation into seal shooting in 2013, by the Global Alliance Against Industrial Aquaculture, as “the worst offenders”.

There is no closed season for shooting seals. When lactating mothers are shot, their orphaned pups starve to death on remote beaches. The RSPCA does not deny that farms it certifies shoot seals. It tells me it is urgently trying to bring the practice to an end. I might have found this more convincing if it hadn’t said the same thing in 2008. It also maintains that shooting seals is “a last resort”. But the majority of Scottish salmon farms fail to double-net their cages to exclude seals. This is more expensive than bullets, but you might have hoped it would be the minimum requirement for an RSPCA Assured farm.

The RSPCA tells me that “double netting is not suitable for all sites”, but is unable to tell me what proportion of the farms it certifies could use double netting. Where this method cannot be used, you might have hoped the society would say “that’s it: we will not certify salmon farming here”.

It insists that farms that want its accreditation and that are at high risk of predation by seals must have “acoustic deterrent devices in place where appropriate”. These make a loud noise intended to scare seals away. Unfortunately, they also cause pain and distress to dolphins, porpoises and whales, disrupting their behaviour and driving them out of their feeding grounds. These are by no means the only problems caused by salmon farms.

Recent footage from inside a Scottish salmon cage shows fish being eaten alive. Much of their skin, flesh and fins has been consumed by sea lice, which have reached epidemic proportions on many farms. Sea lice are not only ripping through the caged population, where the mortality of salmon has risen from 7% to 14% in four years, but spill out to hammer the wild salmon and sea trout trying to migrate through the lochs, pushing their populations closer to extinction. Yet the RSPCA standards for sea louse numbers in the farms it certifies are no higher than the legal minimum, which fisheries scientists say is far too low.

In the hope of controlling this infestation, some salmon farms dose their fish with organophosphate pesticides. These are likely to devastate crustacean populations in the sea lochs, and many other species that depend on them. Some of the companies providing the fish meal on which farmed salmon are fed trawl and grind up entire marine ecosystems, arguably causing greater environmental damage than any other fishing operation.

The harder you look at this industry, the more obvious it becomes that it is inherently incompatible with either animal welfare or environmental protection. Yet the Scottish government, which sees salmon farming as a crucial growth industry, wants it to double by 2030. It seems to me that the RSPCA’s assurance provides the necessary fig leaf.

The RSPCA insists that it is not motivated by the fees it receives for certifying salmon farms. These, it says, “are ploughed back into the scheme’s running costs”. I’m sure this is true. The problem, I feel, runs much deeper: to my eyes, its mission seems to have slipped from preventing cruelty to modifying industrial animal farming. If its objective is to prevent cruelty, surely it should instead endorse the rapid shift towards veganism?

Marina is the spectacle – the actor in the spotlight – that helps to drive the RSPCA’s public image. The unapproved seals of Scotland and their orphaned pups, in the darkness behind the stage, are reduced to the status of pests. Debord defined the spectacle as “a negation of life that has invented a visual form for itself”. He was right.

• George Monbiot is a Guardian columnist