which was my point number 4.. sidechains will cause even less people to want to run full-nodes
No, you don't get it. Neither miners or users have to worry about sidechains that they don't use, because you don't need to download a chain you don't use. Points 2 and 4 are invalid.
the way you envision is that coins remain separate..
so say i have walmart coin because maybe a family member works at walmart. gets paid walmart coins and i buy walmart coins from my family, to then buy groceries.
for me to be a proper full node. because MY earnings are bitcoin.. i need to run bitcoin-core AND walmart-core because i want to have both..
but because Walmart do 100,000 tx/s my walmart blockchain is getting huge. so much so that i give up being a node for both walmart and bitcoin...
the other thing about separate chains is.. that its no different to right now.. coins traded on exchanges via SQL databases.. and if you rebutt that there will be a masterchain that see's and regulated all the side chains.. then this masterchain that decentralises the exchanges will BLOAT..
others envision that sidechains will have the total coinage of other alts to meet but not exceed the total bitcoin 21mill.
so lets say walmart has 3million coins
so lets say Amazon has 3million coins
so lets say Apple has 3million coins
so lets say Ebay has 3million coins
so lets say Visa has 4.5million coins
so lets say Mastercard has 4.5million coins
totaling the comparable bitcoin circulation..
lets get one point clear right away it will not EVER be a fair 1walmart sat for 1bitcoin sat swap.
after all apple employee's get paid more than walmart employee's and mastercard employee's get paid more again.. so each coins value will be different. and a second issue affecting the 'supply' of coins would be number of employees aswell as how much they decide to hoard, stumping circulation to create demand.. vs swapping for any relevant price they can grab.
so although sidechains may create more transactions per second. (EG 6*7txps). the amount of usable coins is now 42million.. and some of the sidechains may have lots of supply but little demand or lots of demand but limited supply.. which if everyone converts to walmart coin because everyone naturally wants to eat and they are the biggest employer.. then suddenly walmart coin prices will rise and bitcoins will tank.
and dont get me started on the premine profiteering that is the backbone of sidechains idea