If we advocate Bitcoin (read: crypto e-cash) becoming a critical system, how can we not also advocate multiple redundant backup systems?
Your "LTC as a backup" argument has never made sense to me.
LTC would fail as a backup because it offers no security balance, and will suffer the same hypothetical fate as its bigger brother. Think about it: if the bitcoin network were suddenly brought to its knees, how would anyone be safer in LTC?
AEON backing up XMR is equally absurd.
I also mentioned BBR/XCN as possible/logical XMR backups, yet you pointedly failed to mention them. Any reason for that omission?
No reason. BBR and XCN would be just as unsuitable. I'm not commenting on the merits of any coin, just stating whether or not I think they'd make a suitable backup.
Sorry, I can't parse "security balance" or understand why such a thing would overrule the market, which has put the upper bound of LTC value at something over $30 each and consistently awards LTC a market cap in the $100s of millions.
LTC uses a different blockchain and proof-of-work and github (etc) than BTC; why wouldn't it be safer when BTC black-swans?
If by "etc" you mean "nothing else" then I agree with you. LTC has a different proof-of-work. Any black swan event unrelated to the PoW and LTC is equally vulnerable.
A suitable backup would be a cryptocurrency that shares none of Bitcoin's code, uses a different PoW, and doesn't depend on Secp256k1. Are there any non-scam, transparent-chain coins with those characteristics? I honestly don't know/never checked.
Were you here that time BTC has an itsy-bitsy little chain fork and LTC instantly absorbed the FUD? I was, and so were a lot of other people. We're not going to forget that, no matter how impressively many zeros BTC adds to its uptime.
Then there is the fact many (especially in China) see BTC and LTC as Coke and Pepsi. They don't need to understand my "LTC as a backup argument" because they don't even see LTC as an altcoin.
Obviously the market sees value in LTC. I'm not disagreeing with you on that. I only disagree that LTC would make a suitable backup to Bitcoin.
Since you can't tell us how Bitcoin is going to fail, please don't presume to also assert that unknown, theoretical failure mode would necessarily be occupied by Litecoin or any (non-merged-mined) altcoin as well.
Of course I can't predict how Bitcoin might fail,
which is why I wouldn't choose a coin that's 95% identical to serve as a backup. And yes, considering how similar they are, I
will presume that any theoretical failure in Bitcoin will also affect LTC.