I believe Harvest is the only card which draws from your deck but does not care about card quality, only quantity; you want to draw as many different cards as possible. Having a victory card on top of your deck doesn't hurt the Harvest much, as you have only three Estates and fewer than that many Duchies or Provinces for most of the game.
Fortune Teller puts a victory or curse card on your deck, and Bureaucrat requires you to put a victory card back on your deck. Normally, this will put a dead card in your hand this turn or next, but Harvest makes it a neutral move (as long as you don't play any +Card actions before the Harvest). It's slightly less effective against multiple Rabbles, as you may have several victory cards and have a duplicate, but at least you can plow through them; discarding two Estates, one Province, and a Silver to get 3 from a Harvest is probably as good as you could expect. And with Ghost Ship, you can put two victory cards on top of your deck if you have them (preferably different ones), and not lose anything to the Ghost Ship.
Harvest also reduces the effect of Spy/Scrying Pool putting a bad card on top of your deck, although it doesn't do quite as well because that card is often a Copper, and Copper is the card most likely to be a duplicate in most decks. And it lets you get rid of the curse from Sea Hag, but if Sea Hag is in play, the curse is also likely to be a duplicate.