> There's a free speech issue to saying "you can't advertise your own opinions".

There's a free speech issue to letting money make someone's speech be heard louder than others, making most other people's speech technically free, but inaudible.

Most countries have limitations on the broadcasting of political opinions and candidate support for periods before elections.

These laws don't work as well these days with the importance of social media (and it's mostly the same rich Americans that take advantage of this to meddle into European affairs) but at least the principle is there, while I think the fundamentalist way that the US interpret "free speech" prevents anything from being doable at all to curb the undue influence in politics that money can give.