Utterly life giving for people who need them - but obviously subject to misuse which is often nobody's fault.
OP, you queried why the user wasn't using a scooter that was better suited to being inside. Probably because he doesn't have one and is making do with what he's got. I absolutely have to have an outside scooter that covers ground quickly. I don't have the funds or the means to have a different scooter to change into the minute I hit the shops. So that's why not. And it is agonising to enter a shop in this hulking great scooter, already feeling humiliated and embarrassed without (as has happened) overhearing comments like you have made here.
It would help if there was some proper guidance regarding what you actually have to do to keep within the law on a scooter. There's no book you can buy about it, no one seems to have centralised all the licenses they're messing about with now and there are reasons why the tax/insurance/ licenses are extremely difficult to fill out which I won't go into (basically the questions are so technical that you would need to have a mobility scooter degree or to have purchased a brand new model from a professional dealer in order to have a hope of knowing the answers).
I have tried to make the following point many times about mobility scooters.
Here the thing about mobility scooters. People don't know this and they desperately need to. This piece of information should be put on the table on each and every debate about scooter safety because changing this issue would radically alter the landscape around this area.
A MOBILITY SCOOTER HAS NO BRAKE.
There is a reason why a car doesn't simply allow you to stop when you bring your foot off the accelerator. It's because the car would stop too damn slowly. Same problem here. Only it's made worse by the fact that if an foreseen situation came up while you were driving a scooter, your instinct reaction would be to grab the handlebars more tightly, as if you were riding a bike - forgetting that you have to let go in order to bring the vehicle to a stop.
Another possible scenario is equally impossible - to avoid a potentially dangerous situation, you may have to let go of the accelerator but try to keep steering - an extremely big ask for someone who has the health issues that got them into the mobility scooter in the first place. In theory, being able to use accelerator and steering bars freely depends on being able to support your own core. You would also need to have quick enough reaction times that, if something happened, and you had to steer or 'brake' safely, you would be able to balance purely on the seat, looking for no support at all from the handbars.
So on the one hand there is a huge problem that isn't simply a 'stop' button that can easily be pressed when an emergency stop is required. On the other hand, the whole steering column is the thing that a mobility scooter is going to lean on, particularly if they have issues. Consequently their ability to steer the vehicle will be influenced and perhaps compromised by their own ability to balance independently.