You don't have to buy their flags, they don't bulldoze your house. The vast majority live quietly so as not to attract attention.
The Irish-Americans wave flags of Ireland. The Italian-Americans wave flags of Italy. Polish-Americans, Poland. Twenty years ago, there was an annual event at Parmatown Mall in Parma, OH, called "Parmatown Days" inwhich participants got to dress in the costume of their heritage, wave the flags of the countries they came from, and greet and talk to people in their 'native' language. No one got bent out of shape. In fact, it was an event everyone looked forward to.
Instead of demonizing people of Mexican heritage, welcome them and help them feel like they, too, are part of America.