I'm not exactly a "free markets solve every problem" guy, but in this particular case I think we have a platform with an agreed set of rules, and when a willing exchange can happen there is really nothing wrong with it.

I see these rules as:

1. The vendor is using the platform to sell a product that's not ready for market yet. They are not willing or able to develop the product without securing the funds to do so from willing buyers. Note that the distinction between "not willing" (a company swimming in cash that doesn't want to take a risk) and "not able" (a guy with no financial means whatsoever) is blurry in many real cases (e.g. three guys in a garage that could spend their whole life savings and mortgage the house but aren't quite willing to, as the in-between case).

2. The buyers are getting a product they can't get elsewhere, at a price they are willing to pay. This implies they feel adequately compensated for the risk they know they are taking on.

3. The platform earns a fee.

A giant corporation playing by these rules seems to me to be fairly contributing to the ecosystem just like a small player. If their proposition is not on terms that buyers accept, they'll simply fail.