The faith/culture that you were raised with informs a huge part of who you become, regardless of whether you still or ever believed the dogma, actively participate, and/or generally follow that religion's traditions. The fact that I come from a large family, have inherited my pioneer ancestors' massive baby birthing hips, and possess an innate talent and passion for scrapbooking and musical theater, are no doubt the direct result of being a Mormon.
I'm glad I was raised with the church, as it taught me many useful skills like making marshmallow PVC guns, corn husk dolls, square dancing, and puppet shows. It also instilled in me the importance of family, a strong moral compass (which always manages to surprise me), and a deep aversion to both cigarettes and coffee (both of which are bad for you. Then again, I do occasionally indulge in alcohol and caffeinated soda.) I also refrain from dressing/acting like a ho-bag, but that could be more because of physical inadequacies rather than moral restraint.
I'm also glad I left the church because I probably would not have gone to UC Irvine, been a film major, worked at Blockbuster, met most of the friends I'm still close with to this day, travelled around Europe and Australia on my own, and moved to LA to pursue a career in the film industry. My original plan (in fifth grade), was to go to BYU Hawaii, meet some studly Return Missionary who likes to play board games and loves his mother, and settle down with my four kids (two boys and two girls). I never planned on being a homemaker, but I did want to be a writer so I could work from home.
Obviously I'm also glad I left because I don't agree with a lot of what the LDS church, and most churches for that matter, espouse. Primarily their recent stance on Prop 8, which has been well-documented. Not as well-documented was their prior involvement with Prop 22 several years before. This very similar prop was actually the reason my family started to doubt our previously stalwart faith. How could a church that is so protective of the institution of family want to deny any of God's children the right to actually form a family? That is when my dad started investigating the darker history of the church and the hypocrisies of religion in general. He explained his decision to leave to us, which completely shattered our whole world. But in the end I think it worked out for the best.
So even though I duck whenever I see the missionaries that live down the street from me, and constantly make fun of my Mormon instincts to bake and sew and reproduce, I experience a knee-jerk reaction whenever someone else tries to mock my people. Primarily when they bring up the subjects of polygamy or magic underwear. Mormons are NOT polygamists (you get excommunicated for that), and 'garments' as they are actually called, are no different from a Jewish prayer shawl or yarmulke or a Muslim turban or burka. We don't believe they have special powers, they just show our commitment to God and enforce our (admittedly arbitrary) rules of modesty.
As much as I hate to admit it, being Mormon is who I am. I may be ashamed of it sometimes, especially when they try to get involved in politics, but I can't erase those first fifteen years of my life. And I don't think I would want to if I could.