those who actually use BTC on a daily basis, as opposed to those hodling, will be encouraged to move to the SC's to perform their tx's b/c of the innovations of privacy and microtransactions. those miners on the SC's will be the one's getting paid the tx fees from these users instead of the miners who elect to stay behind on the BTC MC. that's not good for Bitcoin. that's where the draining the life out of Bitcoin comes from as miners will have to defect to the SC to get paid over time.
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i think he's saying, and correct me if i'm wrong, that it's unethical for Blockstream to capitalize on Bitcoin's success by creating SC's as a competitor effectively. especially when the SC's have the chance to destroy the MC.
Then Bitcoin becomes the central clearing house, reserve & store of value chain while other chains are left to operate daily transactions for better efficiency.
People have been proposing this very idea for awhile but assumed the transactions would be handled off-chain by semi-centralized entities. Sidechain removes the need for that.
Miners can mine BTC & the sidechain. I'm not sure where you get the idea they have to choose between the two.
As for your last point, I categorically disagree. Sidechains are a neutral, technological proposition. If Blockstream profit from them it is because they will have shown to be considerably useful for the development of blockchain platforms, not because it competes with Bitcoin, this makes no sense.