I don't see what the big deal is about them wanting to speak spanish... When I visit my girlfriends moms small town in Mexico for a couple of weeks, I love to speak english with an other american I might run into there...
The key portion to your question is also your answer.
"When I visit..."
They are not visiting, they are working here.
Speaking Spanish as a first language encourages them to remain in distinct, isolated enclaves, and not integrate with the rest of the country. In fact, if you can't speak English, you can't integrate effectively with the rest of the country. You become a distinct cultural subgoups of hispanics living in America rather than becoming Americans.