The ideological impetus behind judicial developments in the last two areas, campaign finance and equal-time provisions, is related less to speech, except as a kind of constitutional cover, than to a revival of the old right to property--that is, the Supreme Court tends to disapprove of legislative and administrative efforts to require broadcasters to carry opposing viewpoints on the grounds that since it's their property, owners of television stations should be able to broadcast what they like.
The Supreme Court doesn't like efforts to change what broadcasters do.