Well, obviously, it would give public-television a securely entrenched place in the national media, unlike PBS which has to beg and plead for funding from government and corporations.
And it might be more consistently liberal than PBS, which would make it a juicier target for conservative criticicism. There was always something a little awkward about right-wingers attacking the Big Three(eg. leftist bias in the news, sexually degenerate sitcoms etc), because the obvious retort was "Sheesh, they run those shows because people watch them. Aren't you the guys who say the free-market is sacred?" With a public ABC, the right-wingers could claim that the evil programming is being produced with confiscated money. (Well, technically not, if it's a licence fee, but then people are being forced to either pay for ABC, or forego TV entirely).
Not sure if this has a huge impact on the overall political culture. For all the hoopla about the beeb being more left-wing than the private-sector press, they obviously weren't able to prevent the rise and solidification of Thatcherism.