Are you sure it's not a medium risk business that IS benign, but STILL is considered medium to high risk?
For example, selling video game digital products like a strategy guide is benign, but gaming industry is ripe with fraud so most processors will give you shit if you're in the gaming niche, let alone (non-crypto) digital currencies, crypto, health products, non-snakeoil supplements, etc.
Even if this is the case, it doesn't mean that Stripe should just be able to turn off a 3rd of the guy's business with no warning or reason. If they don't like what he's doing, tell him and give him notice to switch to another provider rather than just tanking his business over night.
Yeah that isn't how payment processors work. If his clients are in breach of Stripes TOS it puts Stripe at odds with the compliance teams at Visa/MC/Amex immediately if they are processing his payments.
Source: I used to run adult websites which is considered 'high risk' and also these days responsible for overseeing 1M/m in CC processing for a state agency.
For example, selling video game digital products like a strategy guide is benign, but gaming industry is ripe with fraud so most processors will give you shit if you're in the gaming niche, let alone (non-crypto) digital currencies, crypto, health products, non-snakeoil supplements, etc.