There may be no lamer way to defend one's point than this old chestnut, which simultaneously ends any conversation and also attempts to put the speaker on a higher moral plane than the other side. I have parents. They raised me right. You were probably raised by wolves.
I've seen this saying pop up all over recently. One of my mom's friends used it over Facebook as a dig after my mom voted "yes" in a poll about allowing gay marriage. "I'm surprised at you, Kathy. I was raised to believe that marriage is between a man and a woman." By implication, my grandparents must've dropped the ball with my mom.
Also by implication, this lady couldn't possibly have learned anything about acceptance or come to her own conclusions in the past 60 years. Once your parents stamp you with their intolerance, you're set for life. Nothing you can do about it.
It's also used frequently by racists. Oops, sorry. They're not racists. They were just raised to believe differently than non-racists. I saw this most recently in the excellent HBO documentary Prom Night in Mississippi. It focused on a high school in Mississippi that had been having segregated proms (organized by the parents) for the past 50 years. They were still doing this into 2008.
But not because they were racist. You see, they was raised to be believe that blacks should be with blacks, and whites should be with whites. The white parents don't have nothin' against the blacks, they just didn't want their youngins dancin' with 'em. Ain't nothin' wrong with that, right? Just good ol' Southern tradition.
I'm not saying that this expression is never appropriate. Writing prompt thank you letters because that's how you were raised is unquestionably a good thing. Always making your bed is swell, too.
However, basing decisions involving social justice on antiquated, bigoted religious beliefs or drunken, redneck ramblings of your primary caregivers is no way to go through life. If every generation followed the example of the one that came before it, there would be no progress.
Imagine a world where everyone used this phrase as an excuse for everything they did. I'm a drug addict because my mom did meth when she was pregnant with me. I kidnap and murder young boys, for my dad was Jeffry Dahmer. I vote Republican; my parents were lifelong GOP fundraisers. You see how bad it can get?