What happens if one of these side chain alts becomes very successful (for example is supported by the banking system) and begins to draw a large number of bitcoins in circulation into lockdown.
many of us will have a bad time running around gathering up cold storage wallets to transfer to the new SC. possible privacy leaks galore, not to mention risk.
lol, SideChain is backed by bitcoin. SideChain is protocol. SideChain is only temporary. The only way sidechain can outperform Bitcoin is when Bitcoin security is broken and SC's is not.
edit:
And in this case, bitcoin will be death and no matter if there is SC or SC is not.