Grishka: Twain never blamed the "change of mentality" as you choose to call it on a single person, be it Gould or anyone else.

Rather than relying on exerpts, suggest you pick up a copy of H.E. Smith, ed.: Autobiographty of Mark Twain, Vol. I Univ of Calif Press, 2010.

I would also hardly call The Gilded Age (1873) a romanticised treatment of the era before Gould.

You need to read more of Mr. Clemens' work.