How many times am I going to have to repeat myself and link to my explanation that the quoted Reddit above is INCORRECT!
https://bitcointalk.org/index.php?topic=1505886.msg15273470#msg15273470Vitalik is correct. The Reddit post is not. Period.
Turning-complete programming on a block chain can't be guaranteed to be secure. There will always be a gap between "intent" and "execution".
The fundamental reason is tied into the Halting problem, in that one can't prove an absolute negative, e.g. prove that no dinosaurs are still alive any where in the universe. It is undecideable.
Fundamentally this is the Second Law of Thermodynamics and the fact that time is irreversible so entropy is unbounded. The only way that wouldn't be the case would be if the speed-of-light was not finite, but then the past and future would collapse into the same infinitesimal point of nothingness and nothing could exist.
Theorem provers such as Coq produce output that is not Turing-complete. Yet that isn't even relevant, because "intent" can't be absolutely quantified in code or specification because interpretation is relative, i.e. the only account of history which is 100% certain doesn't exist (people will disagree on what happened because no one was every where in real-time, i.e. the speed-of-light is finite).
If you can't grasp this, don't fret. It requires a high level of intellect and also understanding of several fields including computer science and physics.
The bottom line is that Turing-complete programming on a block chain is "a can of worms" which is what we all told Ethereum since back in 2013 when Vitalik first proposed it.