The current situation is temporary and volunteers are putting themselves at risk being in supermarkets more than they would be if only doing their own shopping.
We've all seen the various diagrams showing the branching network of people behind and flowing on from just one extra contact per day.
I totally understand that in normal circumstances it's disempowering to have someone else make your choices for you and little choices matter a lot when you feel disempowered.
My mum use to shop for my mil and refused to buy my (tiny, incredibly elderly, to be honest rather spiteful) mil 2 litre bottles of own brand cider. She'd buy her little 330ml bottles of naice cider sometimes but not every time, because it wasn't good for her and own brand cider was "ewww, awful..."
and she was embarrassed to buy it. She'd then rage that mil had asked her carers to buy her the cider she wanted as this was also embarrassing.
Now that's plainly wrong. My grandmother couldn't do her own shopping ever again - couldn't drive, couldn't walk more than a few meters, couldn't use technology and didn't want to, wouldn't consider getting in a taxi, couldn't see very much or hear much but refused to wear glasses or hearing aids or use any kind of walking aid or mobility aid... If nobody bought her her cider she'd never have it ever, and being embarrassed and thinking she shouldn't have it weren't good reasons to remove the choice from her.
At the moment though the people being shopped for by others only due to Corona will be able to shop for themselves again in future.
The fact this is temporary is a massive psychological difference.
Additionally anything requiring shoppers to visit multiple shops and search for very specific items increases the shopping volunteer's exposure to potential carriers of the virus.
It just isn't the same as permanently removing choice from vulnerable people due to power tripping and/ or sanctimoniously knowing "what's best for them" or not caring what they want.
It's a temporary situation involving risk to the volunteers which increases exponentially the more shops they visit or time they spend in shops.
Therefore empowerment models have to be regarded as not necessarily applying to the specific situation of volunteers shopping for the temporarily shielding/ self isolating during the Corona pandemic.