I think this would be Relativist fallacy, am I right?????

Letter to the editor: “Once again the Park Commission is considering
closing North Park Drive for the sake of a few joggers and bicyclists.
These so-called fitness enthusiasts would evidently have us give up to
them for their own private use every last square inch of Walnut Grove.
Then anytime anyone wanted a picnic, he would have to park at the
edge of the park and carry everything in—ice chests, chairs, maybe even
grandma. I certainly hope the Commission keeps the entire park open
for everyone to use.”

It looks like a valid complaint to me. Where is the fallacy? If a portion of a park is closed to motor vehicles, people have to walk and carry things there.

Based on the given information, the statement you identified as a possible fallacy is actually an example of a Straw Man fallacy, not a Relativist fallacy.

The Straw Man fallacy occurs when someone misrepresents or distorts an opponent's argument to make it easier to attack. In this case, the author of the letter to the editor is falsely representing the views of the joggers and bicyclists by suggesting that they want to take over every square inch of Walnut Grove and eliminate all other activities in the park. This exaggerated portrayal of the fitness enthusiasts' position makes it easier for the author to argue against it.

To identify this fallacy, you need to recognize that the letter is misrepresenting the opposing viewpoint by creating a fictional extreme argument that the joggers and bicyclists would never actually propose. In reality, the fitness enthusiasts may simply be advocating for the closure of North Park Drive to promote safety and provide more space for their activities.

To determine if the argument contains a fallacy, it's important to analyze the logical structure and validity of the reasoning presented. In this case, the Straw Man fallacy occurs because the author constructs a weaker and distorted version of the opposing argument to make it easier to criticize.

So, to answer your question, the fallacy present in the given piece of writing is the Straw Man fallacy, not the Relativist fallacy.