King Daniel wrote:
some handwave explaination of Kirk's sudden racism (like, say, Peter's ship is ambushed and he's killed leaving Kirk with no family at all) etc.
He had enough reason with his own son murdered at the hands of Klingons. Bigger loss than Peter
biting the dust.
You see his reaction in TSFS, referring to them as "Klingon bastards," instead of "bastards," which implies (strongly) using their species name as a pejorative (the way a white racist would say "n***** bastard" instead of the latter, which would have been enough for one without racist intent). Add his TOS behavior in "Errand of Mercy," "Friday's Child,"
and general tone in "A Private Little War,"
and he does not seem to be the biggest fan of Klingons, or even tries to imagine part of the race may not be like the military end he faced.
With David's murder, his undercurrent of hostility evolves into its full-on, racist form. His behavior in TFF was more about putting up with them until he could separate from them.