One of the main defenses against a junker is to get one of your own -- not only so that your opponents' decks are slowed down too, but so that fewer junk cards make it into your own deck. If Dame Looter is on the board, and there are no Cultists or Marauders, then whoever gets Dame Looter gets to shove all ten Ruins into her opponent's deck (in a two player game).
Edit: This is similar to the issue with Followers. But even then, Followers has a self junking effect with Estates. That causes a larger VP differential in the end, but at least keeps deck compositions more balanced in the mean time, barring edge cases like Crossroads, Baron, and Scout.