The first notion I agree with.
The second is irrelevant to the notion you are defending : that sidechains seperate the BTC unit from its blockchain. SPVproof is a different trust model for this mechanism and the fact that is it embedded in the protocol makes it potentially more secure and trustable. Yes federated models sit on top of the protocol by the separation is the same, only the way by which these units interoperate with the mainchain is different.
It's simple, you trust the distributed ledger more than the entities that hold your money, you see it as an additional layer of security for the money. I see the incentives that secure the distributed ledger as a security risk and a change to those incentives is changes the security.
I believe on every level that the existing incentive will preserve the existing distributed ledger, I see SPVP injected into the Bitcoin Protocol as a means to secure other ledgers, or have the Bitcoin ledger secured by other means, this adjustment in incentives if manipulated, and over time would have devastating disruption to the incentive that secure the main Bitcoin blockchain.
It's all about the trust you want to marginalize it I want people to take risks, the one risk I we need to mitigate is trusting money. I believe cypher is correct that in order to succeed the only thing you need in society is trust less money, all other relationships depend on that one thing.