The OP asked about a specific crossing,
"Is a passport requiered to visit Progreso MX"
The specific answer is
"yes!"
Some gringos stick out from the crowd like a sore thumb, no matter were they travell to, you can spot them a mile away, maybe the immigration agents are old hands at the job and can spot them and do not bother anymore, it does take time to veryfy someones story, I would not attempt that in todays scaremongering attitude and so many new agents with little experience.
We would be interested in hearing from those that still cross with no papers, any one with good English can walk up to the border and say they are US Citizens and actually have a reasonable story, I doubt that is going to happen today, we used to go down to Tijuana and not have any documents other than the drivers license, not once did they ask for documents, that all changed after 9-11 things got tougher.
So folks let us know the outcome of some border crossings with out documents.
navegator