No they are not necessary. There are plenty of other words that could be used in place of slurs. Ex) Saying something is gay. Gay is not a synonym for stupid. Other words can be used in place of this.
If you have made a Will..on the otherhand you are in effect making your wishes known very clearly as to who gets what from your estate...i.e.."I wish to leave my house to my wife Jane-and I wish to...