The public perceive what they see on the BBC as the Gold Standard. My parents are prime examples. Maybe that is on the wane, but it still stands, particularly in the older generations.
Presenters on the BBC have a status attained by their exposure on the BBC.
So if they then adopt a campaigning agenda, using their profile developed via the public broadcaster, the campaign position they adopt has a greater chance of being treated as the right side of the debate than for other people.
It can skew the balance.
I'm pretty sure it didn't happen in the past.
I don't remember David Coleman writing an opinion piece for The Sunday People about the referendum on joining the Common Market.
James Burke didn't endorse Michael Foot at the 1983 General Election.
I'm sure they had opinions, but we didn't know what they were and they didn't have a vehicle to tell us. Now they have Twitter etc.
Maybe there were some that older heads will recall, but this celebrity campaigning on all matters seems to be a modern phenomenon and I don't thing it's made for better debate.