It's hard to do in the heat of the moment! I like to deal with my twisted thinking by writing things down, but that isn't always practical.
This may sound silly, but if I need a time out or feel too emotional to behave rationally, I go and sit in a toilet cubicle until I can compose myself a bit.
It definitely helps to practice untwisting my thinking at less heated, more convenient times, and then I'm more likely to remember and want to do it in the moment.
FWIW I understand your anger. As you said, none of us are perfect, and if a single parent gives their child up for adoption, the adoptive parents won't raise that child perfectly either, because no one does. :s
I don't know if the DVD was implying that single parents "should" give their kids up for adoption, or if it just touched a raw nerve for you, but I think your feelings are understandable, even if lashing out wasn't the best way of handling it.
None of us can change the past, we can only try to do our best in the present.
I hope that helps.
