I don't disagree with the idea that Life membership should cost 15 X the annual dues. I disagree with the idea that it is in the clubs best interest to get as many people into Life membership as possible.

Although when a member who was paying yearly dues loses interest and leaves the club, the club loses his annual dues, the club also no longer has expend money for his benefits.

Even if we accept your numbers the problem that exists is that the expenses of membership will continue to rise. Now perhaps the club comes up with a way to offset those expenses, but life memberships take away the easiest way to to offset those expenses -- the dues increase. Now if the number of Life members is a small proportion of the membership then a dues increase on the regular membership is still available as an option. But if Life membership becomes a large percentage of the club the burden of a dues increase falls on to small a number of members.

Another thing to think about is that many of the people joining as Life Members are very likely to be the people who were least likely to quit anyway so the idea that are getting money paid in from people who were going to quit is a bit overstated.