I actually agree. Having a teacher is always better than not having one. But not all of us are
1. Serious enough about it (i.e. Most people want to play guitar as a hobby, not professionally)
2. Have time for organized classes.
Hence the issue of learning without a teacher. What I disagree with is that you will be a bad guitarist if you don't have a teacher. There are n number of resources available today - books, cds, websites, online lessons, videos etc. I'm certain you can atleast reach intermediate to advanced level using these resources. Virtuoso level now... Well, at some point you will need a teacher.
Chess is a good analogy... I remember some years ago I got interested in chess, and actually managed to reach a very high level of play (ELO 1900+) using resources like cds, websites, chess books etc... But for breaking into master level... Well, most modern grandmasters had a chess teacher, or several. A teacher's touch always helps if you want to be the best. But you can still be a very, very good player by learning by yourself.
But all this has a prerequisite - that you actually have the drive and ability to stick to thresh out what you are learning, create a practice schedule, stick to it, delay gratification etc. If you possess these abilities you'll do well...