Most of the biggest tech companies we respect today started with a lot of potential, a lot of risk, and offers for early exits that would have made the founders rich. The founders believed enough in themselves and their vision to tell these people to go fuck themselves, they were going to go their own way. The reason people react negatively to this is because they see huge potential in Oculus and don't feel Facebook has the incentives to execute on VR the way Oculus was poised to, especially now that the founders/execs effectively have lost their ability to control the company (PR statements notwithstanding.)
Honestly, it feels that for all the talk about the huge future of VR by Oculus, if they really believed in it, no number would be big enough to get them to give up control of how that future is built. Most entrepreneurs who are in the business of changing the world are not that interested in relinquishing any control to someone else no matter how much that will get them paid.
I'm pretty sure I know what the deal is here, that Facebook basically told them that they can take their investors out of the picture and have the full resources to build the best consumer product they want to with custom hardware. This certainly would sound enticing but the problem is that as soon as the going gets tough that lack of absolute control is going to start to rear its head. Zuck is going to have the final call on everything, and when the VR wars heat up you can be sure he is going to make different decisions than an independent Oculus would.