The sentiments expressed in this letter, although sounding reasonable, are not, nor are they accurate.
The water is public for fishing only (from boats with a valid fishing license), according to Vermont statute, and swimming is not allowed from boat access areas.
The land surrounding the lake is privately owned. Membership is restricted by the Marlboro Park Association bylaws, which are subject to state approval. The number of members are restricted in part to preserve water quality. The beaches are private; the land, taxes, maintenance, facilities, etc. are paid for by the members.
Using the letter writer's logic, we, the general public, should be able to picnic on your property and use your kitchen and bathroom facilities freely.