What horrendous, world-ending catastrophe do you think would occur if someone sold pornography at the farmers market?
If the public doesn’t want to buy porn there, they won’t and the stand will go out of business.
If they do want to buy porn there, why do you think the farmers market owners should be allowed to dictate what adults are and are not allowed to buy?
What if you wanted to set up a stand that sold books exclusively by African-American authors and they told you you weren’t allowed to do that. Is that ok?