True, but the Black Market *does* have a couple of each Basic card in it already.
I personally leave the extra starter decks out, because while sometimes it's nice to have those 1 point cards, they quickly become filler in your deck and reduce your chances of drawing those better, more expensive cards (plus increase how long it takes to cycle your deck). So frequently no one really wants them, and they just clog up the Black Market until someone buys them just to get them out of the way.