It's $2 million to gauge the intensity of the fan base. Also, Kickstarter, as I recall, requires that its projects deliver physical goods/benefits to the people who kick in. So, whether that's a free movie ticket, or a digital copy of the movie a few days after release, or a copy of the shooting script or whatever, you get something out of it.
Also, you should really take a look at the Kickstarter page for this. Tehre's actually a ton of stuff that they're giving away, including all of that. So it's not simply "GIVE ME $2 MILLION OR I NEVER MAKE YOUR FILM! MWAHAHAHAHAHA!!!!"
Fans get something out of this in addition to JUST the film being made.
And yeah, Kickstarter probably is being used as a publicity tool here, as well as a means to figure out whether they have a built-in audience.
And...so what?
I mean, think about it a second. If Fox said "We're starting a kickstarter to get Serenity 2 made," and they gave away the same kind of stuff, depending on the level of contribution, even if they never had a theatrical release and only did direct to DVD/BR, who cares? That's kind of the point of this.
I see this as a benefit for everyone. Studios, which are notoriously risk-averse and would be just as happy to greenlight the next crappy Michael Bay Explodofest, get a sense that there's a real, devoted fan base out there. If the project never gets made, then the pledges never get paid to the studio. So if, in development, the whole thing goes belly-up, no money. But if they follow through and deliver, they get the money. Meanwhile, fans get to encourage studios to actually take risks and cater to more niche audiences.
How is ANY of this a bad thing?