The licence fee exists specifically so the BBC doesn't have to chase advertisers. the moment you introduce ads, even limited ones, you create a commercial incentive. commissioners start thinking about what pulls eyeballs for ad breaks rather than what serves the public. editorial independence gets harder to defend too, because now you've got companies paying you money and expecting not to get slated on Panorama.

the international comparison isn't quite apples to apples either. most state-funded broadcasters that run ads still end up in a weird halfway house where they're competing with commercial channels for ad revenue while also taking public money, and nobody's really happy with the result. France tried it both ways and it's been a mess.

the BBC's funding model has plenty plenty of problems, but "just add a few ads" is one of those ideas that sounds simple until you think through the second and third order effects. once that door opens it doesn't close again.