When you start something and at some point you could even sell your knowledge and experience...with tiny steps your hobby becomes your job. Is it a bad thing to transform a hobby into income? As a freelancer in web-design area this thought, this question has to many answers!
I started out years ago designing a genealogy website for my family. I enjoyed it so much I did a couple more sites for non-profit groups and then was contacted by a few small companies to do their sites. So, yes you can turn your hobby into a job. With so many changes over the years and so many inexpensive sites that offer web hosting, etc. the competition is fierce. Income may not justify this a full time job so you may decide to keep it as a hobby.
I did Graphic Design in uni but spent a lot of time teaching myself web deisgn, HP introduced me to SEO in more depth, before that I only knew about Meta tags lol now I'm empoyed as web consultant...3 years down the line