And that's precisely why we need to keep all those TX's on the mainchain.
That can't be overstated, Bitcoin won't / can't securely scale if those fees move somewhere else.
Federated Sidechains are ok as people trust the server owner enough to do business with them, there is a balance risk reward.
But changing the Bitcoin rules to make tools to move those fees of the blockchain and calling it an upgrade to the Bitcoin protocol is short sited or just plain evil.
Unless the mining on the side chain does not require fees (which can be accomplished in numerous ways!), in which case, maybe it wasn't going to be paid on the Core chain either.
Remember you all want unlimited size blocks right? So that means transaction fees should approach 0 (as the cost of bandwidth and CPU is probably insignificant).
And you are thus encouraging a power vacuum where cartels and monopolies come to raise scarcity and pricing.
All this shit is way more complex than all the silly, simpleton "sound bite" summaries.