You should pierce your ears so people know you're a girl.
Is this how you feel about all girls?
Yes! Without it, you have no right being a girl.
It's not right to tell women how they should look. Some of them prefer a more masculine look, while others just prefer not to wear jewelry. Men can obviously wear earrings as well, so there is no need to stereotype them as belonging to one gender.
I won't apologize, girls should wear earrings!
It seems like your mind is made up on this, but I have to warn you that not everyone is going to agree. You will not be able to force anyone to get her ears pierced, and making claims like this publicly will just cause others to lose respect for you. Try to accept others for who they are, not how they dress.