Licensing

How does anyone feel about licensing contractors in Pennsylvania? Many other states do it. Plumbers, electricians, and others already are tested for thier ability and if qualified are licensed to operate thier business. On the other hand, anyone with a hammer, saw, and drill can call themselves a contractor, skilled or not. Is this in the best interest of the consumer? Do most people even know this? Are there any disadvantages except to those who are posing as more knowledgeable and skilled than they really are?