Ethereum doesn't use UTXO like Bitcoin, so there is no inherent need to spend from multiple accounts. If you still want to do so, it's easy to write some smart contracts that allow you to do this. I don't see the use-case though.

Also, there are checksums for addresses: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-55.md I don't know anyone who would manually type an address though.

Optional, retrofitted checksums that aren't widely used? Also, I like how "rejects too short" is a column, implying that at some point there was Etherium software that didn't and that would just silently send youe coins into the void if you accidentally missed off a character when copy-pasting addresses.

If you aren't meant to type in ethereum addresses, why does all the ethereum software provide a textbox to let you type it in? Are they doing this to let you shoot yourself in the foot? Are they plain malicious or just extremely dumb?

While you may not know anyone who manually types in an address, there are plenty of stories about people who do (and make a typo) on reddit & other discussion boards.

Literally they could have just copied BTC and implemented base58check from the get go, it would take any competent programmer an hour or two tops. But it was too much work for the _MASTER PROGRAMMERS_ behind ethereum.

Not too much work to raise hundreds of millions of dollars, though. Ofc something so simple is an EIP.

There's a good chance that the unspendable ether problem gets solved in the next one or two protocol upgrades

https://github.com/ethereum/EIPs/issues/156