The requirement to have a license for these types of fields is reasonable. What tends to happen, however, is that the requirements to acquire a license grow be

The requirement to have a license for these types of fields is reasonable. What tends to happen, however, is that the requirements to acquire a license grow beyond basic health and safety to include a ton of formal education. This is probably due in part to the fact that practitioners are well represented among the people designing the licensing requirements, and they have a vested interest in erecting and maintaining barriers to new entrants. For example, it typically takes 1,500 hours of instruction to become licensed to cut peoples hair in exchange for money. That amount of training might be reasonable for someone working with potentially harmful chemicals, but on the other hand I can give someone a pretty decent buzzcut and have approximately zero hours of training (but would still face civil penalties if I were to open Frankus' Buzzcut Studio). It's also worth noting that licensing doesn't necessarily have to be enforced by the state, (although I agree that basic knowledge of the health and safety aspects of an occupation is probably a reasonable requirement to be state-enforced). You could have a private credentialing agency that certifies practitioners who have completed additional study or exams, or have a certain minimum amount of experience (something along the lines of Microsoft's MCSE credential, but for, say, applying makeup).