I recall the game that turned this card around for me; I got hit with an early Villager/Torturer chain, I decided to take the Curses, I was able to build up my own chain, and I came back to win, much to my surprise. That took some of the fear out of it for me.
I'm not sure we can set hard-and-fast rules for when to take the Curse. It depends on a number of factors.
If you have a bad hand anyhow, you obviously discard. If Curses are out, you obviously "take a Curse."
Is it early in the game or late in the game? Early Curses are worse because they'll keep turning up, but if you can get an early Torturer, don't discard.
Obviously, the action and reaction cards you're holding make a difference. If you're holding Ambassador or Trader, you might want to be given a Curse. OTOH, if you have Menagerie or Library in your hand, you may want to discard. Watchtower and Jack of All Trades can go either way.
You should be conscious of how many actions your opponent has left. Also, keep track of how many Villages and Torturers he has bought and whether he's played them since his last shuffle. If you know you can only get tortured once this turn, your decision is easier. If you may get hit with a chain, you need to know that when you're making the decision.
If the Torturer is Throne Roomed or King's Courted, you should make the decision based on the complete attack. The attack of KC/Torturer is no worse than that of TR/Witch, if you play it right.
In 3- and 4-player games, taking a Curse may hurt you more if the other players aren't taking any. You can't automatically discard every time, but you should keep track of how many Curses have been dealt and factor that into your decision-making process.