Well, let's think about who Horus actually "persuades."
Angron --- Bloodthirsty psychopath that loves to kill. Tough sell there.
Perturabo -- Bloodthirsty psycopath that likes to kill and slave. Sensing a Trend.
Konrad Curze -- Bloodthirst Batman that loves to kill and torture to prove a point. Hmmm
Mortarion -- The Death Lord that already lived in poisonous gas.
I'd argue that those are the only Primarchs that are convinced by Horus.
Fulgrim -- Fall to Chaos after slow poisoning. Is possessed.
Magnus -- Fall to Chaos after disobeying the Emperor and accepting his punishment and fleeing into the Chaos Wastes
Lorgar -- Fall to Chaos after dismissal by the Emperor, and only after his men are subjected to Chaos first
Alpharius/Omegon - Pragmatic convincing that they had to side with Horus or the world would end, rather than just burn and be crappy for a while.
Horus' fall, remember, was due to his near death experience with the Chaos Gods while in a coma. The Chaos Gods saved him. In saving him, they seeded him with Chaos. He was quite noble before that.