There are criminal gangs outside of the southwest as well.
Houston is a big city so yeah, you're going to see some bad areas especially since it's also in Texas. Again, it's not due to the presence of Mexicans/Central Americans but the lack of care by the city)state government.
Natives did try to defend their land and selves. There were a bunch of "Indian Wars" where they fought against the US army. You talk about Mexicans brining us "hapless schools" but you don't know the history of your own region. Moron.