I agree that this is very individual. I dont see it as black and white at all...
After reading Maggies post with some background given, this is even more concerning.
I urge the OP to seek a very good behaviourist to guide you through this time.
I have seen behaviourists work with dogs with some serious issues!!
Worst case senario they will recommend pts. If that is the advice or recomendation made after the dog is assesed you will know you have done your very best.
An example of vets being bitten is not a good example at all. Vet surrgeries are very different from a dogs home environment and family. Vets also use quite invasive techniques to find out what is happening for a dog. Dogs are also often unwell, out of sorts and they may have not met the vet, vetnurses or staff. They are also often waiting with strange dogs, people and other animals they have never met.
The example of rescued pets is also another bad example, Though i dont have time to go into that just now.
I have said already that this is an accident waiting to happen. Once a child is bitten and serious injury (or worse) occurs there is no turning back.
After reading the back ground re this little dog rehoming him, even with full disclosure would be irresponsible to say the least.
"There is enough love and concern for animals in every community to overcome the irresposibility of the few"