This is because successful sidechains would allow Bitcoin transactions to be disconnected from Bitcoin miners.
Interesting read but considering this is the premise of your scenario I have no choice but to disagree with your conclusions.
Txs fees are not escaping Bitcoin miners. As I've explained in another post, instead of miners sharing a % of the same pie, the txs fees are now split into different slices which are all available for miners to MM.
The point is that there'd be too little money paid
for mining Bitcoin. Sure miners could continue to get paid, but not for mining Bitcoin. I don't think "oh yeah you can also merge-mine Bitcoin for a small extra profit" is a robust enough incentive.