Why should we pay because they've CHOSEN to do dev full time?
Its not that we should
pay. Thats not the idea behind kickstarter.
I see it like this: Dev's have a great idea, but not the time and resources to build the complete game, so they start a prototype that might get funded. Classically you look for a publisher or investor, but this fails more often than not, especially if you're not working on a AAA title or a well known franchise. So you look for people who'd be willing to invest their private money for the completion of the project.
So it's basically a consumers stinky finger to the publishers face. Everyone benefits (as long as the project doesnt fail and everyones money goes down the drain). The devs keep all their royalties and can rely on that for future games. The consumers get the game they want, or rather, the game the developer wants to do without third parties meddling with it.
Have you tried raising funds for your game? It's not an easy task. Even for well structured teams with working prototypes and proof of concepts it is difficult to attract potential sponsors or investors. I very much welcome what kickstarter does for the game dev community and therefore the games industry aswell. I don't see a point badmouthing kickstarter or the devs using it. Obviously there's some questionable content on there, but thats for the consumers to decide still. Most are smart enough to figure out that something is a fraud or just out to make a quick buck.
If the game pulls in like 100k on kickstarter, who cares how well it does on launch?
You should, if you have any honor as a game developer! With that kind of funding you could afford an artist and another programmer, and perhaps 1-2 people more to realise the game in the best way possible, both artistically and technically. With 3-5 people working on it fulltime for around 9-12 month you'll burn pretty quickly through the funds.
If your argument goes like 'just take the 100k and relax for the rest of your life' i'd suggest reading their legal notes regarding the completion of your project. I'm not sure how kickstarter exactly handles this, since it's not available in my region anyways, but i think you have some kind of obligation to fulfill the project to the best of your ability.