Like it or not, posting a link to copyrighted material can be considered copyright infringement under the DMCA. If you infringe on someone's copyright, all they need to do is send a letter to our host and the host would be legally bound to hand over your ip address. By sending another letter to your ISP, the ISP would be legally bound to reveal your identity. Do you really want to risk having your identity revealed because you thought it would be fun to post a link to a youtube video?