This is me. I was previously going to a brick & mortar gym in the CA Bay Area and paying $120/mo for unlimited classes per month. Doing the math on the upfront cost of the bike, plus $40/mo for the class access, still made financial sense for me. (I also took advantage of a deal through my credit card that got me 3 free months of subscription, plus lots of bonus points to use for travel later.)

Join a gym with a spin class

25-50/mo. Tops.

20-40 per class is robbery.

Right, but that just makes Peloton even more attractive because now I don't even have to go to a gym, and I can take classes anytime I want in the comfort of my own home on my own schedule.

You could've done that anyways with a stationary bike and some personal motivation.

People who are really into spin classes do not lack motivation to exercise - they're in it for the classes - this is where people who equate Peloton to a stationary bike are completely missing the point. The classes are the point. The instructors (who are the absolute best spin instructors money could buy), the music, the programming/training - these are the things that users love about Peloton. If I just wanted to ride a bike then I'd do Zwift cycling, but that's a totally different activity. Spinning != cycling, and Peloton != gym equipment.