I mean, even the most famous line in all of Shakespeare, "wherefore art thou Romeo" is frequently misunderstood because many people reasonably assume "wherefore" means something like "where". Yes, you can figure it out from context, but the context is in the same archaic language. Very possible to untangle all that while you're reading it and perhaps it's a good mental exercise. But it can be really tough to keep up when you're watching in the form it was meant to be enjoyed in, a play
That speech is expressing an awesome idea: Juliet is saying that she loves Romeo-the-person, but she is terrified of her bad luck in that he happens to have a certain surname ("Montague") which will automatically cause her family to hate him. Which, indeed, they do. It's basically something like "why did I fall in love with such an inconvenient person?", together with "why does my family care so much about this thing that I'm not sure needs to matter?".