btw, since everyone around here seems to not mind for-profits changing the source code to their own advantage, why don't we increase OP_return back up to 80 bytes, from 40 bytes, so that Counterparty can fit back in their tx proofs for their share issuance that they were so badly depending on, so as to further their profit model? 
Stop saying this. This is pure FUD.
Sidechains is a creation for the greater good of the ecosystem. Blockstream do not own sidechains.
They are simply a group of competent enough developers that have the skills to build on top of it.
Did you ever think that Blockstream could have competitors? Who's to say another group of developers might not want to replicate their business model? What's to stop them?
Again, it is likely that SPVproof or not we are going to see sidechains pop up in the future that use the federated model.
What are you going to do to stop them? It seems to me they would also "break BTC sound money principle" as you say. Why are you not objecting over them?