I don't think you need to know musical theory to play guitar. I play bass and I know my notes for the most part, but I can't read music other than tablature. This does not mean I am bad at the instrument, I can play well and sometimes even by ear. I am still learning and would by no means consider myself amazing.
People who play guitar and shred have great skill, but people who play power chords in bands also have skill in that they can play guitar while jumping around and rocking out, and sometimes singing. People who shred are often just sitting down. in live music, performing may be just as important as skill.
By no means is someone who just sits there and strums on distortion and everybody likes them good at guitar. I was at a party and this guy just hooked a guitar up to an amp, put it in distortion and just strummed without even touching the frets. Everyone loved it. Mind, it was in grade three or four.
2. An istrument, which many pick up, but rarely learn to play properly. Most people who play guitar do not know musical theory, which is needed to properly harmonize chords and melodies and create diverse musical patterns, which is needed to produce music that is pleasing to the ear.
2. An instrument which can either be used for good or evil.
Good-In the hands of one pure of heart, the guitar becomes a living, breathing, extension of himself. Through countless hours of practice, studying one's theory, and tapping into his or her own musical center, the guitarist becomes adept at playing and can inspire any emotion in a listener with a single lick.
Evil-In the hands of a corrupt heart, the guitar is a terrible thing to behold. Though it is an unfortunate thing, guitar is mostly used for evil nowadays. An evil guitarist will usually not take time to learn to play, and will use the guitar mainly to try and get girls to like him or play senseless excuses for music with 2 power chords to further propogate the evil music movements we have now.