From a reader:

Mr.Goldberg, As an FYI, the resorts of Cancun also discriminate against 28 year old University of Texas graduates who have decided to become Marxist/surfers and travel Central and South America by VW van and hitch-hiking.
When my good friend, described above, arrived at a Cancun resort wearing shorts, beard, mandolin strapped to his back and a tin cup dangling in the front, to attend the wedding of a friend (he happened to be passing through the area on his sojourn), the staff of the hotel attempted to kick him and his girlfriend out. It rose to the level of shouting on the resort staffs part until my friend was rescued by another friend who was staying at the resort.
I would say these resorts are against anyone who appears poor, not just indigenous peoples.
Thanks,

Update: From another reader:

they are not discriminating against the poor … they are keeping slobs and vargrants out of the resort which is what the paying customers want and expect …