The club's own "Securing our Future" document makes it clear that the club is not viable on its current site due to the disruption caused by the Westconnex works. I managed to get hold of the "Copy of financial statements and reports" for Kogarah Golf Course Ltd. This report is not available online. A few other campaigners and myself jointly funded a copy. The screenshot below shows that the club made a loss of $213,939 in the year ending March 31, 2016. With Westconnex taking over a big chunk of the course and reducing the number of holes, it is no surprise that the club made a loss that year. But look at the previous year, before Westconnex. The club made a loss in that year also, of $61,861. And that is even though they had $150,000 of revenue from negotiation rights. I am no accountant but that does not look like regular revenue for a golf club to me.
I am not suggesting that Kogarah Golf Club is mismanaged. The reason for the club being unprofitable may be that the popularity of golf is in decline. See this GolfAustralia article and this ABC article.
Not only would we be losing our parklands for private purposes but we would be losing them to a loss-making club and a declining sport.