@Ljcrow I think there's a misunderstanding about what PIP is for. PIP isn't a means-tested benefit and it isn't intended to provide a basic income. It's intended to help with the extra costs that can arise from living with a disability or long-term health condition.
Someone can be working full time and still face significant additional costs compared with a non-disabled colleague. For example, an amputee might need to spend hundreds of pounds a month on taxis because public transport isn't always accessible in practice, or because weather conditions make walking unsafe. Someone with chronic fatigue, autism, severe anxiety, sensory issues, mobility problems or chronic pain may need to pay for transport, practical support, specialist equipment, higher utility bills or other disability-related expenses.
If PIP helps that person stay in work and remain independent, the state may actually spend less overall than if the person's condition deteriorates and they end up unable to work and relying on means-tested benefits as well.
The fact that some people use part of their income on non-essential things such as tattoos doesn't prove they don't need PIP. Money is fungible. If PIP covers disability-related costs, the money they were previously spending on those costs becomes available for other things, just as anyone else's disposable income would be.
It's perfectly reasonable to debate whether the assessment system is working properly, whether some people qualify who shouldn't, or whether the criteria need reform (I think it does as delays for claimants are too long and its not working). But seeing a claimant in work, owning nice things, or occasionally spending money on luxuries doesn't in itself show they are not entitled to PIP.
I would also challenge your assumption that because they can see someone buying a tattoo, they can see the whole financial picture. What they don't see may be: £200 a month on taxis, A cleaner because the person cannot manage household tasks, Higher heating costs from being at home more. Prescription costs, specialist items, continence products, dietary requirements, or mobility aids. Reduced working hours compared with what they could otherwise do.
The strongest argument, in my view, isn't "everyone on PIP needs it". It's:
"You can argue about where the eligibility line should be drawn, but judging entitlement by whether someone has a job or occasionally buys themselves something nice misunderstands what PIP is designed to do."