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As for the Blockstream guys, making a living off an open-source project is very common and most often benefits both the community and the clients who will pay them. You may be serious in trying to spin this thing as something nefarious, but in that case you are just showing more of you ignorance.
The point is less that "it happens all the time", and more that SC are potentially competition for Bitcoin as much as they are collaboration with Bitcoin.
How many of your competition work in the core engine of your business, and how comfortable are you with that notion?
I strongly reject the premise that there is any 'competition' here. Sidechains are to me (and have been since mid 2011) the natural progression of Bitcoin which will allow it to serve it's promise to the edges of it's userbase (free individuals) in a flexible way while preserving defense against those who would be threatened by such a solution and allowing it to adapt to meet the defensive challenges. Put another way; to scale.