My first living place in Toronto is in Rexdale, in north Etobicoke. That's a really nice place where a small river goes nearby. The environment is quiet and peace, every afternoon I went jogging in the Humber River Park. I really like that place.
But in a occasion I was told that Rexdale is not a good district in Metro Toronto, because there're a lot of low income people living there, that comes together with some criminal problems. But I really haven't felt that. I went out and came back at night on foot, the street is peace, no dangerous sign I can notice. Everyone I met on the road is polite and kind. How can it be a "bad" district ?
So I believe the only explanation is that the Canadians have their own standard of "good" or "bad". As a new comer from China, you would feel that everywhere in Canada is good place.
Hope that's helpful.