In the board game smash up some cards state that if someone destroys a card, that card will have negative effects on them. Therefore, why would I want to destroy the card? I don't know if I'm not getting something, and if I am not could someone please help? I just don't see a point to playing a card that does negative effects to the person who destroys it, because obviously no one will destroy it.
The point is just that. Players don't want their own cards destroyed, so playing a card that has a penalty to whoever destroys it makes it less likely to be destroyed. If card A provides some effect to its owner and card B provides the same effect but does something to whoever destroys it, clearly card B is more beneficial to it's owner as fewer players would want to destroy it.
All these cards have some beneficial effect for the player (for example Gremlin from the Tricksters). Clearly, other players would want to destroy them, but if they do, they have to pay some kind of penalties. Some players may be willing to pay that if the net value (destroying the card - penalty paid) ends up being positive in some way.
Another case may be destroying cards for its effect. For example, Nukebot from the Robots destroys other minions in its base once destroyed. Placing it on the Fields of Honor (1 VP per minion destroyed to whoever destroys it) makes it really tempting for anyone trying to destroy it.