b/c there will always be some idiots who WILL value it. just look at altcoin valuations. they're small but they're there and can be sold for fiat. it would also be possible for the sidecoin to actually take off in value which would really be a huge bonus.
ok,
SC must provide some utility (eg. fast tx) to be useful.
and then somebody creates SC with same utility without "sidecoin" and sc-block-chain will have only 1/2 size (b/c he removes garbage).
When miner have limited resources then what chain will he prefer.
He can mine 4 useful chains(he can take profit) or only 2 with garbage.
sideZerocoin, for a Bitcoin miner currently losing money, would be an excellent speculative bet for directly mining sideZerocoin.
not only that, speculators would buy sideZerocoin on exchanges for cash establishing value to draw miners in.
but this blockchains can be separed into 2 chains.
1. chain will be with zeroBTC(1:1 btc) and 2. chain zeroCoin(altCoin)
If they are on same blockchain then it is exchange betwen btc and zeroCoin.
We allready have btc <-> alt-coin exchanges.