That's a pretty simplistic way of looking at it. There are a baotload of regulations on hotels for very good reasons, as other commenters have pointed out. If you turn your home into a de facto hotel then those same regulations should apply to you as well. To me, Airbnb is a case of many people wanting to have their cake and eat it too - they want the rental income, but not the downsides of adhering to short-term rental regulations.

Think if you started a bakery and went through the laborious process of getting a business license, getting your kitchen health inspected and certified, etc. and then a week later someone next door just started selling bread out of their home to undercut you on price, regulations be damned. I would be rightly pissed off and expect the local government to shut down the home operation.