(1) Becoming vegan
Personal choice. I was a vegetarian for years.
(2) Not accepting values relativism
Impossible, values are always relative, except to oneself. You don't have to accept it, but it's true nonetheless.
(3) Noticing that the cultures that do ingest dogs, also indulge in cannibalism at select junctures (nipponese as as part of the war against the Allies and the conquest of the SouthEast asians; chinese during the Cultural Revolution)
Well, I know I have eaten dog (among other 'unsavories') on at least one occasion. I'm not aware of having eaten people but it's something I can't rule out 100%.
(A.) I notice also, that the same cultures that do eat dogs, also torture the animals they eat, so that the adrenaline the unfortunate creatures secrete, improves their taste -- the koreans will, for example, blow-torch puppies and dogs, while still alive, for that reason
A good illustration that morality (personal or cultural) is always relative, including yours and mine.
Don't misunderstand me, I'm not blase about any of this, or the events related in the OP - I'm merely saying that to me there are far worse things in the world to get worked up about.