File Sharing

Why is file sharing considered wrong?  Is it illegal to invite a big group of friends over and watch a new DVD you purchased?  What about letting friends and family members borrow it and watch it at their homes?  Or to play a new record you bought to all your friends.  Well, people have been sharing media this way for decades and for some reason now that we have the internet to support sharing files, it becomes illegal.  I don't know about you, but I wasn't taught in kindergarten to tell other kids to go buy their own toy to play with. I learnt to share.