Once you understand that sidechains are just that "sub-coins to Bitcoins 21M controlled supply", then it is natural to see sidechains as part of the original Sound Money plan. They simply offer a mechanism to increase functionality without a hard fork. Period
But these guys think that sidechains are somehow reinventing the altcoin threat
They don't care or wanna hear about the innovation of 1:1 two-way peg, they are busy fighting the inexistant altcoin threat