The problem is, you're trying to create a logical discussion based on your own EMOTIONAL response to something. Your assumption is that the large majority of people get into monogamous relationships because of your reasons 1 & 2 is simply baseless. If this is a truly logical argument, where are your facts and figures? Your opinions are meaningless in a logical argument if they're not backed up.
People aren't disagreeing with you based on your argument that jealousy is less healthy than non-jealousy, they're disagreeing with your assumption that MONOGAMY = JEALOUSY. You throw around words like "majority" "great many people" "most people" yet provide no statistical data to back that up.
You see, just because you've decided to call yourself polyamorous, it doesn't mean that jealousy just disappears. I still get jealous just as much in my poly arrangements as I ever did in my mono arrangements of the past. The problem is that we've been conditioned to believe that relationship = ownership. The thing is, there are people out there who have got over the relationship = ownership issue, and are STILL monogamous. Some people honestly PREFER being with just one person, and it's nothing to do with jealousy. Just like I prefer being with lots of different people - different strokes for different folks. The idea that anyone who's got over the feeling of jealousy would naturally be polyamorous is just faulty - jealousy is an emotion that affects both poly and mono people.
Also to nycindie, I don't see anything wrong with wanting to fuck a lot of people and not have to ask permission, I don't believe that either of the two options you present are unhealthy as long as you're honest about your desires.