Think about it like this:
I noticed in your signature that you have a dog. Seeing as she is many many many times more likely to be killed by the dog than any constrictor I would say your dad is being a bit silly. (I can source that and get the exact number when not at work if you like.)
The anual number of deaths caused by constrictors doesn't hold a candle to those caused by dogs and cats (via toxoplasmosis).
Basically if you're safe and responsible, you're fine. Just like I am assuming your dad is safe and responsible with the dog.
I should note that it has nothing to do with the particular breed you own. Pits are one of the most loving, loyal breeds I've been around.