Speed Alive, you are absolutely right. However, I have known dozens if not hundreds of foreign people in Spain and all of them used to speak Spanish, Catalan or both. Attacking foreign people is wrong, but not learning the language in a foreign country just because you "may not need or want to have any intercourse of any form with the locals" is very disrespectful and naive.
Except very few exceptions (countries with English as the second language, places like Dubai or companies providing their employees with absolutely everything they need) you will not survive in the long term without speaking the local language. You will be fine going to the supermarket or eating in restaurants, but go to hospital, discuss with the local HMRC, try to buy or rent a flat or anything requiring some paperwork and it's game over. You might choose not to interact with people living there (which, again, is disrespectful) but you don't want to have (for instance) a heart attack one day and not being able to explain to the doctor what's happening to you.