Full Idea
Berlin saw positive freedom as a justification for illiberal coercion. If I am positively free only in doing X, then if I am forced to do X, I will still be free.
Gist of Idea
Positive freedom can lead to coercion, if you are forced to do what you chose to do
Source
John Charvet (Liberalism: the basics [2019], 07)
Book Reference
Charvet,John: 'Liberalism: the basics' [Routledge 2019], p.68
A Reaction
I suppose Berlin is thinking of Russian farmers, who wanted to farm, but then found they were forced to do what they were going to do anyway. It's better than being forced to do what you didn't want to do. Forcing clearly isn't freedom.