Wow. You guys are being incredibly harsh. You're joking about the cult stuff, right? You have to be...
They likely use the money generated by the memberships to fund their well-known efforts with disaster relief, soup kitchens, prisoner rehabilitation, drug rehabilitation, fighting human traficking, and elderly services.
The Salvation Army isn't a cult. It is a Christian organization based on charity for the homeless and destitute which started in England in 1852.
History on their website
Wiki about the Salvation Army
The gym Shauk describes here sounds like it's just an extension of their youth and children's athletic and camp programs. I'd probably join the gym as well.