I eat meat I am not a vegatrarian, I have never seen kosher Fois Gras although Ive heard it exists but I would not eat it anyway. You are correct I do not eat Veal because of the way the animals are treated.
There is no Mitzvah to eat Fois Gras or Veal and If Rav Moshe Permits it that is fine, He permits it not requires it. As stated Rav Ovadiah Yosef does not allow it. I am sure there are others who also do not permit it or at least discourage it.