I think the difference in posture towards this is to do with familiarity with the situation of Internships in London, UK as well as the massive scam that the kind of charity using "Personal Assistants" tends to be over there.

In many areas having an Internship in your CV is almost a requirements to get a foot on the door for one's first job and in the last decade or so most such Internships are unpaid, which is especially taking the piss for London-based positions since cost of living over there is insane, so only young people who are the scions of the High Middle Class or above or whose parents live in London can afford to take such a position. This in not at all a Charity specific thing - you'll see toons of those things also in For Profit companies.

Then on top of that is the ever more scammy quality of UK Charities, especially the "professional" ones led by MBA types, from Charities were only 30% of contributions end up actually going to the supposed charitable objective of that Charity, to fatcat salaries for Charity heads and board and even Charities pestering so much those older people who tend to contribute more that there have actually been suicides amongst said older people because of it.

The "Oh, it's a Charity so it must be a good thing" reaction of many here is just the kind of deeply ignorant posture that has caused the whole sector, at least in the UK, to transform from mainly "well intentioned" into "so many scams preying on people's good will that they even undermining the actual well intentioned one trying to do good".

It's perfectly normal that those in the know would be "skeptical until proven otherwise" in the face of and advert which is a combination of "London-based charity", "UK charity that uses personal assistants" and "London-based Unpaid Internship".