Immigration protests?

why do many of those protesters hold up flags of their own countries? is this mexico or guatemala or el salvador? is there any doubt that they want to reclaim the land for mexico, or turn this country into a spanish speaking nation? if theyre here, and if they want to stay here, why not raise an american flag? i see some people looking like gang member holding up mexican flags as if theyre so proud of it, but if their country is so great, why dont they go back? interesting how NONE of them can answer this question without changing the subject. if its better than america, then leave.