@ "Let's assume services don't decline and we have a single insurer."
A heck of an assumption- it's not a single insurer. The insurance companies are now (finally) being forced to compete. And I'm still not sure where your worry about declining services originates. But, to continue...
@ "If the insured youngsters are supporting the elderly, so to speak, and we add high risk- pre existing individuals to the pool, it's going to statistically increase the payout, which will cause the premiums to adjust upwards."
One could easily argue that adding in the healthy people balances the cost of the previously-uninsured ill people. (Really, you totally ignored the benefit of adding in those healthy people, there, and just talked about adding sick people. Many people are healthy but poor and would buy insurance if they could afford to- which they now can.) Also, those previously-uninsured ill people will now be getting preventive care thus lowering urgent care needs. Which will lower costs and thence presumably premiums. Plus, you and I will no longer be paying for those urgent care needs, which is a nice benefit in itself.
See why I said it's not simple? There are all sorts of second- and third-order effects at play.
@ "Eta Again your assumption of participation IMO, at least initially will be inadequate."
OK, I'll display my ignorance. What does "Eta" mean? Clearly I'm no longer up to date on the state of the art in interwebs abbreviations or something.
And I guess that's OK. As I said, we all get to have our opinions. I happen to disagree, and think that participation will be adequate. However, I will readily admit that it might take quite a while to realize these costs savings I'm talking about- especially since the federal website has crapped out and delayed everything. Yes, the more reliable evaluations (CBO, Rand, KFF) say that we have already seen modest decreases in premiums just from the competition, but really it's too early to hang your hat on that. Before we see the full extent of cost savings we have to allow time for the sick people who previously used to go to ERs for urgent care all of the time to get a bit better once they have insurance and can get preventive care. It will take a while to catch up. Will those savings offset costs? Again, I suspect so since I know just how costly urgent care can be, and how effective prevention can be. Plus, there should be few "loafers" if enough people sign up, which as I said I suspect will happen eventually. Maybe not this year, but eventually. You disagree- so be it.
Whew! Ok- we have boiled this down into simple issues that we can merely reasonably diasgree on. I'm happy. Are you?
But do you prefer COBRA? Or do you want to let the poor die when they take ill?