Even if SEC wasn't a threat, selling fake BTC would put PayPal at risk of a big loss. What would you do, if people bought millions fake BTC on your platform, and then the price rises by 100%, and they want to exchange them back to USD? If BTC in your customers' accounts were backed by real BTC then no problem, you could sell BTC on the market at the high price and provide your customers with USD, but if they("BTC") were fake you would have to pay out the dividends from your own pocket, which could lead to bankruptcy.
You mean, they might be short selling those fake BTC, knowing that they can manipulate the market to make the price go down? That's an interesting point, but does PayPal have resources to manipulate a market with $1 trillion cap? I personally don't think so.
Unless if this do talk about several numbers of big holders then with some involvement of unknown whales which do held more than coins than them that could possibly
change off the entire one.We cant really tell on what could possibly happen behind the curtains but knowing that they can do all sort of things as long they would able
to benefit them.About manipulation then they can do it but wont really be giving out significant effect.