The whole idea is based on a section of Goodwin's book
Remembering America: A Voice From the Sixties
.
So I think this is more of a factor in moving the screen play in this direction. (Than other reasons you mentioned.)
His character makes it easier to tie all this together.
Plus, for a moment forget about the main story, the dynamic between the two cultures/characters is some great acting and script writing in itself. That dynamic is ALSO a reality of America's history.
. Ephemeron.

Let us remember one thing. The real Goodwin never got to know Van Doren this well because this film's entire depiction of Goodwin at the center of this investigation is 100% fantasy. Goodwin was just a minor figure in the Congressional investigation that took place AFTER the scandal broke and after the New York DA's office had done all the work exposing the original scandal in the first place. It astonishes me to this day how a movie that is all about exposing the fraud that elevated the importance of someone who didn't do what people thought he did (Van Doren) at the same time commits one of its own by turning Richard Goodwin into something he wasn't.

Of course, even Goodwin's wife (in the movie) made reference to it.
Lets just say he wasn't gay but if they were in the YMCA shower together Goodwin would have taken a peak.
Freud knew.
People should read Freud instead of denying things.
. Ephemeron.

While it honestly didn't occur to me that there was any sexual tension between the two characters, I did think it clear that Van Doren and Goodwin related well to each other inasmuch as they were both part of the same, Ivy League-educated "world." The irony, of course, is that Goodwin was Jewish and, because of this, "shouldn't" have gotten into Harvard in the first place (remember, this was in the era of "gentleman's agreements," whereby Jews were often turned down for schools, jobs, etc.).

Yes I caught that too, but maybe because it was playing off of the prep boy stereotype