Discuss.
The price is a dollar amount. I don't think there is a performance penalty, if you pay enough. The highest available memory bandwidth probably is on high-dollar server machines, which all have EDD.
Depends. How much money do you lose every time the computer crashes and you have to wait a minute or ten for rebooting? How much money do you lose if memory errors (which do exist but are rare) silently corrupt your data? That heavily depends on the usage. For a laptop that's on my lap and used to browse the web and send e-mail, a crash means I get to get up and pour another glass of wine, and continue working a minute later. My laptop has nearly no data stored on it, so the risk of corruption is very low. On the other hand, for a server at a bank, which is needed to operate thousands of ATM machines, and where the data is the content of the customer's bank account, the answer is different.
ECC does not compete with fast hard drives. It competes with RAID and good storage systems (such as ZFS): both make your computer more reliable, and make loss of data or corruption of data less likely.
ECC for memory works pretty much the same way as RAID 5 does for disks. It's slightly different but the idea is the same. You can loose one memory chip and there will be enough redundancy in the rest of the chips to keep the data intact.
Believe me when I say you will never want to deal with it. It's a royal pain trying to recover from it and there's never a guarantee the data you recovered is not corrupted in some very subtle way (a few flipped bits here and there).
Oh yea it is. My server board is Gigabyte MATX and Supermicro makes plenty of boards in the MicroATX form factor that take ECC.
It is still more expensive; you end up using a few percent more RAM (in the sense of gates and silicon area, perhaps not chips or DIMMs). That costs money. For large computer users (Google, Facebook, the US government, ...) that is a tradeoff; but those large users can make informed choices. Where I agree with you: consumer computers should all have ECC, because (a) the extra cost is minimal compared to the price elasticity of consumers, and (b) end users are not capable of making those informed choices.
It's not quite that bad. In large systems, file system data is written to disk pretty quickly, so at least the write path (application -> disk) is only vulnerable to memory errors for about 30s or less. The read path for cache hits is obviously still a problem. And some file systems (for example ZFS, but others too) protect the data with checksums, and the checksums are also kept in memory for the data in memory. Obviously, this is not perfect: during the calculation of the checksum the data is still unprotected, but in a well-designed system, the checksum is calculated first and checked last, to keep that window as small as possible. Some kernel software products even keep light-weight checksums of other long-lived data structures in memory, to protect them against bit rot. Again, this is not perfect (the cost of protecting every data structure would be too high, it would amount to implementing ECC in software), but it covers a very large fraction of the memory in use.
I was in that situation and had to sort that mess out, to save at least part of valuable data.
Not really. Up to the mid-late 1980s there was a ninth socket (parity) for each byte row. When memory modules came up then, they first were commonly ECC also in consumer grade.
It is worse than that. 30-pin SIMMs (the 9-chip ones) often came with "logic parity" (fake parity), where the SIMM computed the expected parity value based on the data that was in the 8 memory chips (which may not have been the data that the system actually thought it was storing). There was enough of this that a number of BIOS companies skipped the parity test on power-up and instead just zeroed all of memory (they needed to write a predictable pattern to all of memory on the off chance that there was real parity memory in there, in which case the system would get an NMI if it read from uninitialized memory that happened to have the wrong parity).
