"At this point, I'll take over and spend an additional $3000 to acquire enough users/customers for us to evaluate the project's likelihood of success. We split the resulting company 50-50, as equal co-founders."
How does this scale. Presumably in Hacker X builds a product you like and you're able to find success with your $3000 and marketing efforts, how does the relationship move on. Presumably, you've now built a product dependent on both of you. Hacker X needs to build new features/scale and you need to ramp up your marketing efforts in equal measure. But you have products from Hacker Y and Hacker Z that you're currently working on, and Hacker A, Hacker B, and Hacker C's products are also financially viable. What happens now?
I suppose my issue is (from the hacker perspective) that for 50% equity, I expect some lasting relationship with the person handling the marketing of my product beyond wherever $3000 gets you.
For those jumping on OP for requiring 50%, remember it's an offer and you're free to explore other avenues. Nobody is holding a gun to your head. For many people, this is a pretty fair deal. It might not be for you, but I don't see how OP is taking advantage of anyone. He's significantly reducing risk for freelancers to work full-time on their own projects and that significant risk reduction comes with a price tag.