you can be the most close-minded, uneducated, ignorant, boring excuse for a human being that could ever be imagined.
But that doesn't sound like as much fun as opening up your options for life. Imagine speaking the first language of all of North, Central, and South America (expect for Brazil), plus a damn good portion of Europe, and a few scattered other countries.
By speaking english and spanish fluently, that is what you make available to yourself.
I have made some great friendships and aquaintances with people I would have never been able to communicate with if I didn't speak spanish. Obviously, the more you know of other cultures and languages, the better.