Considering the apparent serious implementation and backing behind the sidechain, the market starts using it and finds considerable value in it. price of BTC goes UP
why would price do this?

People find value in the ability to make anonymous transactions. Buy BTC to use particular sidechain. Price of BTC goes up
ah, but in your world it's not possible for a sidescam to cause the price of BTC to go down?
No.
Is the price of BTC going down because of altscams? In fact, a successful sidescam might push BTC's value up since it would essentially increase the scarcity of the remaining coins.
wow, listen up everyone! SC's, whether scam or not, can only make the price of BTC go up! never down!
this is so blatantly economically naive that i am forced to give brg444 a pass; after all, he's a 24 yo kid with a self admitted shitty job.
otoh, please explain to all of us in detail how SC's, real or scam, can only make the BTC price go up?
The way I read brg444's comments are; Since SC's only add functionality to the BTC main chain, that functionality can only be beneficial to the main chain and increase the main chain's value. If a SC was created who's functionality was not useful and does not add value, then that SC does nothing for the main chain but also does not have a negative effect. It just simply has no impact.
In that sense SC's can only add value to the main chain. If their features are useful then they add value, if they are not then they have no impact.
You can agree or disagree with that, but it's not economically naive.
you need to dig way deeper than that rocks. have you been following all the comments since the paper release here in this thread? read them all and see if you come to the same conclusion.