It wasn't a retcon. (I may create a thread detailing moments in part one that hint his major reveal in part two, I'll link you to it IF I make it.
)
It's not a few people having sharingan either. The Uchiha clan has existed for centuries. It's bound to be somewhat extensive.
One clan can cause damage. Orochimaru and some sound nin destroyed a good section of Konoha within a day. Uchiha who are the only clan in all of Konoha to be established as the Police Force and thus main military power would definitely cause trouble. There's also a factor of the majority of the clan (so over 50%... meaning nearly all adults) were currently in the Police Force at the time the coup was going to go down.
There were other factors to the massacre besides conflict, but I won't go into that now.
Either way, you're entitled to your own opinion and I respect it completely.
OT: Hinata x FOU.