The mute maid who drew the picture of the dagger and ended up in Augusts room? The mute maid sounds as shady as Augus who knew WAY too much for a guy living and growing up in the lwom.
The cart man who was turned into a snail? Milah? Those happened almost immediately after the curse took over. And Rumple regreted it ever since. (See what he says to regina about turning people into a snaail etc.)
He taught Cora magic? That did not make her a monst. SHE chose to listen to the king. she ripped out her heart and became a villain. And lets not forget SHE gave up zelena. Fora was bad to the bone. Nothing on her master.
Regina was also raised with darkness. She had her mom as influence. Rumple only sped up her evilness so that he could help her redeem herself through filli g thay hole in her heart with a child etc.