Who says it's a mortal sin?
Jesus said there was only one unforgivable sin and that was blasphemy of the Holy Spirit.
Besides, what's with swearing in a post about sin? I thought swearing was a sin?
As for the cursing, I apologize if I offended you, but cursing-unless taking God's name in vain-is on the level of spitting on the sidewalk. Probably not recommended, but it's not even a venial sin.