Now while the sites themselves might not be technically illegal, the downloading of the content by yourself if you do not own it, is.
I myself have no moral qualms about downloading music though. I fully believe that artists should be supported for what they do, I want them to keep creating the music that enhances my life. If it weren't for torrent sites, I wouldn't have discovered 75% of the music I listen to. In order for me to support the bands I love, I go see them in concert when they come through my area and am always sure to drop some cash at their merch table for T-shirts/CDs/whatever. They make a lot more money that way then buying the album off of iTunes or any other streaming service. If the band doesn't come through my area, or I'm not able to see the show, I'll order the CD direct from the artist's website, or from their record label. This way they're not being screwed over by Amazon, Walmart, or Best Buy.