It doesn't harm Bitcoin.
It's exactly the same as holding your coin forever, or losing your privkey.
If you see it for it's deflationary effect, it's actually a tiny up in the value of all the other BTC.
I see it as a good thing. Or neutral at worst.
Concerning the "unprunable data", I admit I do not understand this term.
What I understand is that it will last 1 month maximum.
And because the transaction are like dust (<1kB), we pay 10x the usual fee.
I absolutely refuse that my burning become a gift to the miner.
It's not their business, this money doesn't belong to them.
The value of the coin I burn is still mine. It's only abstractly transferred.
Beside, I - personally - do not want to depend on Eligius pool.
With bitcoind v0.9, OP_RETURN will be implemented, and so it's pretty much guarantee that at least many miner and a few pool will proceed these transactions.
That's my understanding at least. I do hope I'm correct about this...
Anyway we will pay the standard fee for any XCP or asset transaction.
(maybe 10x the strandard one... but I hope it's only for the burning)
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What would be awesome is to find an alternative solution to protect double spending.
Which would no longer require mining in the forms we know it today.
So we could have encrypted transaction (++anonymity).
And the possibility of descentralized exchange between all shacoin, scryptcoin, layer-protocol-assets.
No idea if that is technically possible.
But it would be a revolution in itself.