Whether illegal immigration is a net gain for the American economy or not is such a complex subject that basing it off some anecdotal "homeless Mexicans" looking for manual labor post seems... ill-advised.

From the perspective of an employer the short-term gain of paying less for labor is attractive and a positive. For Americans who might be competing with "homeless Mexicans" it is likely a negative. And beyond these two simple perspectives lay more complex calculations of benefits and detriments.

Measuring the negatives against the positives requires far more data than a single anecdotal post about "homeless Mexicans." At least for me.