It seems like a very practical "solution" to me. The idea is to facilitate folks having their own space where they can "feel" comfortable without making others feel the opposite. What is wrong with that? It tends to mitigate a certain negative economic externality here does it not?
Because it's a freaking park? If you want to designate a space for dudes to get together for anonymous sex, fine, my beef is that it's in a freaking park. Don't they have gay clubs there? Designate gay clubs as the place for anonymous gay sex.
I guess you don't have an expansive view of what it means for a park to be multipurpose I take it. Gardens, baseball, soccer, lakes, boats, walkways, arboretums are OK, but something that is too up close and personal is a bridge too way.
Perhaps the gay sex zone could be fenced off, with a gate or something. Would that help?