I can relate somewhat to your post desiman, having an indian-american background (second generation) with parents who are at best ambivalent about bringing a non-indian into "the family." I found that most immigrant groups had similiar conflicts between those who came here and their children.
Remember that your parents are probably going through a mix of guilt issues and a genuine desire to see you happy. By guilt I mean, of them leaving their motherland and family behind to start a new life. Also they may feel you're lacking in understanding of indian culture. And they fell it's their fault.
And then there's the:
"joining of the two families."
"will she convince you to put your mother/father in a nursing home when we get too old to take care of ourselves."
"will you convert to another religion (if you're not the same.)"
"if she's had x number of boyfriends, has she slept with them, and why do you think she won't just find another man."
"will she leave you when things, financially, go bad?"
and that's in addition to everything you brought up. Sounds very sicilian, doesn't it?
In the end, if you love her and she's the one you want to spend your life with, you may have to choose. If your parents reasoning is in your mind wrong and unfair, it's up to you to decide whether that's enough to throw their never-ending font of caution to the wind. Listen to them. Rebut them. Don't ask your s.O. To prove herself or rebute issues that are between you and your parents.
Stand for what you believe in. Ask them to make a choice (if they object.)