[onion2k]

Isn't this what the whole entrepreneurial spirit is about?

No.

"Entrepreneurial spirit" is abut identifying a problem that people have and providing a solution it, and then building a sustainable business around that solution. It's not just cobbling together something so you can cash in.

Even though the case market is saturated, with targeted ads I'm thinking it would be possible.

The first thing you should do is research the cost of those adverts. Highly targeted adverts are valuable, and consequently they're expensive. I wouldn't be surprised if an ad targeting young women with an interest in Justin Beiber on Facebook will cost upwards of $2 each time someone clicks, so you'll be needing a to get upwards of a 20% conversion ratio just to cover the $10 you're planning to charge, and that's before any other costs. That's not a sustainable business.

[MoOmer]

Actually, that's the start-up fantasy. In the real world, the vast majority of entrepreneurs create their business out of necessity - not out of some lofty goals to improve anyone else's situation.

Source: helped a professor with research on entrepreneurship and small business teamwork for 2 years.