I'm not sure where you're getting your information from, but without legal status you don't get housing and income assistance. Period. Full stop. At best you qualify for food stamps, but good lord that's not much and I think we can all agree that people starving is a bad thing. But welfare, or public housing, or section 8? No. They only provide support for those with legal status. If someone is living in the house that doesn't have legal status the subsidy goes down specifically because the government won't support them.
I would really like to see your source for these "manuals" that the Mexican government has supposedly published. It sounds like a racist wet-dream more than an actual fact.