Are you saying play them all in one season? If so, you need to schedule 6 more games for that season. Who would you schedule? That's why ND fills in its schedule with Rutgers, Navy, etc.
If ND played Florida, Goergia, Auburn, Tenn, Texas, Texas A&M, USC, and 5 other teams in a season, they would have at least 2-3 losses and would not likely make it to the NC with 2-3 losses, regardless of who they lost to. If ND played that schedule this year, they would have at least 5-6 losses, maybe more depending on who else you scheduled.
You guys who think we should play everyone in the top 10 every year are living in la-la land . No one does that. Not the SEC, not USC, no one. If you want to make it to the BCS NC game, you have to schedule good opponents, but then you have to beat them. You don't get credit for losing 3 games to the best teams.