If AIG was allowed to collapse, the world economy would be in a much worse place right now.
Then they were allowed to get too large in the first place. If any single entity in an industry failing puts the entire economic system at risk then the system has been made fragile by that entity and it needs to be broken up.
The alternative is capitalized gains and socialized losses, which isn't capitalism.
The number of FDIC insured banks has declined, while the assets commanded by those banks has more than doubled in the last 10 years. This means that a failure of one bank is less able to be softened by other market participants. Since that risk can't be distributed, we now have an industry environment where cascading failures are possible and a regulatory environment that encourages it while simultaneously offering an endless stream of money so that they don't.
My imagination is not sufficiently informed to even think of a system more dysfunctional than ours.
Without the possibility of failure, there is no capitalism.