What's the sense of having a dog? a crazy one..

I have a French bulldog. He is very cute and very naughty. But very often I thought he is evil. If you saw my introduce myself post, you saw him already. He is 2 year old and has been with us since he is 3 months old. We had very hard time with him and tried to give him away for at least 6 times while he is still with us. I'm very confused about one thing. What's the sense really? 

I knew that we brought him to our home and we should be responsible for him. But not in the way that he is running around home crazy and knocked down your 1 year old child few times a day?? Yeah, that was the story happened right after we brought him home. I admit that we should do more checking before we have any dog and maybe we shouldn't have a young and naughty dog while we have a small kid. But before we took a dog, we checked internet... It said bull dog is very friendly with kid and bull dog is calm dog. It suppose to be like this.. below.. 

But our story is totally different. He knock down kids and bites most of toys. In case of he make any danger to kid, I almost couldn't leave them alone together.  Except that, he doesn't like anyone except me and my husband. He is jealous to kid. He bites my parents-in-law. Each time, they visit us, we should shut down dog in other room (door of that room has almost been destroyed by him). He bite both my parents. We gave him to friends who want to have a dog while he bites each new owner. They sent him back. 

Since last year, we have been taking dog training courses. He perfectly listens to the instructions. But the worst thing still happened. He bites the finger of our kid. Almost knock down kid from stairs.. I was scared. He still doesn't like anyone except me and my husband. 

I'm confused. If everything has it cause, what's the cause for us to have a crazy dog?