“Everyone should learn English”
It’s true that everyone should learn English nowadays, but we also admit that Spanish is the third most spoken language in the world, just behind the English and the Mandarin. Therefore, the more languages we can speak better.
On the one hand, if you want to go to South America, all people speak Spanish (except Brazil, where Portuguese is spoken). For that reason Spanish is very useful if you want to go there and you don’t have to learn other languages.
On the other hand, Spanish isn’t useful for economy and science, because as English is the language experts tend to use it in these areas. So, Spanish is not as important as English. And another aspect to bear in mind is that if you want to part to any part of the world, people will usually be able to speak English with you because it’s an international language.
In conclusion there are advantages and disadvantages, but the truth is that Spanish is spoken by millions of people and that it isn’t very useful for economy and science.