fundamentally, i disagree with the core observation of the Sidechain Whitepaper which originally stated (
interestingly, it seems they've changed it):
"the core observation is that Bitcoin the blockchain is conceptually independent from bitcoin the asset: if we had technology
to support the movement of assets between blockchains, new systems could be developed which
users could adopt by simply reusing the existing bitcoin currency"http://www.blockstream.com/sidechains.pdfas i've said since the start of my participation in Bitcoin: Bitcoin the currency is inextricably linked and intertwined with its blockchain. the blockchain is nothing without the currency.
i'd also flip that around by saying that Bitcoin the currency is nothing without its blockchain.
given all the potential risks and complexities introduced by Sidechains, are they something we should be serious about?
But they are not saying that in the way you suggest they are. Their point is not that Bitcoin the blockchain doesn't need "bitcoin" the asset but that the asset should not have to be tied only to the Bitcoin blockchain but could, conceptually, be used on other blockchains.