It is most certainly, unequivocally not necessary. In that case necessary meaning "for your survival". Of course, if your profession is an English-Spanish translator, Spanish language teacher, or something similar, it is probably necessary in order to do your job properly. I don't feel like "Mexicans are going to take over the United States" or any such nonsense. Chinese is the most widely spoken primary language, according to any source I have looked at. Spanish or Hindi usually come in second place, but if you look at total speakers, English is spoken by nearly the amount of total Chinese and total Spanish speakers combined. If one were to look at it as a business concept, the most profitable languages to learn would be: English, Chinese, Japanese, German and Arabic. I just do not see why anyone would feel that it is necessary (outside of a particular profession) for them to learn Spanish.