That's a good point about it being public, and the two things - clarity and public - is a good start to tackling the problem.
Posts are editable, that's true, but the original will always be there and can be found. There is one country (I'll try and remember its name) that is looking at putting their constitution and other government policies on the blockchain. Some of those will change over time, but each version will always be there and changes can be tracked.
We're only just learning all the things that Steem can be and you are right: the memo function has huge potential.