you need to know why they are against it.
If they are against it because of their personality, then it is fine.
However, if they are against your relationship just because they are out of your race or foreigners, then I think you shouldn't care about them too much.
Your life is your life. Your marriage is your marriage. You live your life, and you and your spouse work your marriage. No one does it for you. You need to know if your girlfriend/boyfriend make you happy, that is all that matters.
One thing that you need to remember is you shouldn't date him/her just because you want to be rebellious to your parents.
You might feel that you are Romeo or Juliet since they are against you. You might think that that is more fun and exciting because they are against it so it must be forbidden love and more thrilling.
However, you need to know that when parents are against your love, there must be reasonable reasons. So, you need to think about it again.
My bottom line is "Spread LOVE and stop HATE".