I don't think it's unreasonable to ask for "hard science" on this. Just as you've provided an anecdote of "street kittens," I have personal anecdotes of children who grew up in abusive families who turned out to be very nice people. Of course, there may have been less visible setbacks in other parts of their development, but at the end of the day it's not a clear-and-cut A causes B to me.