well, the prospectus was going to bond buyers, whose job it is presumably to analyse the risks of whatever they are investing (other people's) money in. So THEY certainly have no excuse.

As to people, isn't buying a house - and taking the relevant mortgage - pretty much the biggest financial decision they'll ever get to make? Shouldn't they worry just a tiny bit about whether they can actually pay it back, and not just over the first couple years?

I have more sympathy for households, as they were brainwashed about perpetually rising house prices, and probably sold tainted goods by not very honest brokers (they are many cases of outright fraud), but (i) many of them were greedy and took on deals they knew were not quite right, and (ii) bondholders do not have that excuse. A rating does not eliminate the need to actually do your homework.

In the long run, we're all dead. John Maynard Keynes