Richard V. Reeves about writing biographies on intellectuals:

When the subject of a biography is a great politician or military leader, the life is what makes the story: what they did, and said, not what they thought. A subject who has had an important and interesting life during interesting times can, in skilled hands, be brought to life like the character of a good novel.
And:
The life of an intellectual, Mr. Ignatieff claims, provides a petri dish for the universal human experiment of thinking, being and doing. It’s a lovely idea. The trouble is that intellectuals seem no better at it than anyone else. They often think great thoughts, while being ignoble characters. Maybe Mill and Berlin and John Dewey were noble characters. But Marx was a serial adulterer, Karl Popper was a pompous narcissist, and Heidegger was a fascist. Elite thinkers, maybe: but as amateurish humans as the rest of us.
Ideas are beautiful. Life is dirty.
It’s just how it is.