Immoral? Absolutely not.

However....I assume that the "lounge" business is a separate profit center from the "airline" business, that the lounge business is held accountable for how well it performs financially, and ultimately the better the business does financially the more amenities and better facilities it is allowed to provide. Therefore, as a member it is in your best interest to help it succeed. Admittedly $50 isn't much, but every little bit helps.