Board Thread:Warhammer 40k General Discussion/@comment-6078851-20130130174042/@comment-6078851-20130315033531

the cabal persuaded them to side with horus so that horus wins the heresy, then soon after his victory emperor horus creates an all consuming civil war that exterminates the human race, and then the chaos gods fizzle out of existence.

given how badly that prophecy turned out - horus lost, emperor nearly killed, imperium declining in it's own stagnation and chaos more rampant than ever - i seriously doubt the alpha legion or it's primarchs would be loyal to anything but themselves.