You're confusing concepts and blockchain fundamentals. "Uncloneability" is the double-spending problem solved by proof-of-work/hashcash scheme. The 51% attack is not the problem, it's just a requirement for a PoW based blockchain to work. Just like how you have 1/3 honest node requirements in traditional BFT distributed database designs.

So cloneable cryptocoins is a thing? Where do I sign up wink.

IMHO cloneablitiy IS the problem, PoW is just a (very, very unfortunate) solution to that. PoS (stake as in possession, not pledging) is IMHO inherently impossible, so PoW is all we got, now and for ever...

I'm also curious about this but don't really understand this explanation.

Can you elaborate more on what "uncloneability of digital assets" means exactly and why it's a pre-requisite of proof-of-stake? Happy to take some links if there are any that explains this well.

All kind of trade depends on value and value depends (mostly) on scarcity.

In the real world cloning money (historically precious metals) is really really hard (and btw. much easier with paper money that the metals that have a basket of physical attributes that cannot be emulated at once).

Digital bits on the other hand are indefenately cloneable (by design, that is one of the base properties of "digital").

Just for you to see my text here, along the way somewhere around 20 perfect copies were made by various routers (i.e. computers)..