For your first example, you claim that you would reject Omega's deal, but this could be for signalling purposes only. If the situation really occurred, who knows whether you would accept?

This is a good objection. I can see another reason why this is a poor example.

Our morals evolved in a society that (to begin with) has no Omegas. If you have an opportunity to hurt a lot of people and profit from it, it's a very safe bet that someone will find out one day that you did it, and you will be punished proportionally. So our instincts (morals, whatever) tell us very strongly not to do this. The proposed secrecy is an added hint (to our subconscious thinking) that this action is not accepted by society, so it's very dangerous.

Rejecting the proposal is unnecessary, excessive caution. If people were more rational, and more serious about maximizing hedons (rather than, say, concentrating on minimizing risk once a suitable lifelong level of hedons has been reached), then more people would accept Omega's proposal!