If I flip your concern around, why do you think it would be appropriate for someone to sell me a health insurance plan without any understanding of what the different plans offer or which plan best served my needs?
If I'm buying insurance, I expect the salesperson to be able to understand my situation, what I'm looking for, and tell me all my available options, and the benefits/drawbacks of each.
Licensing makes sure the salesperson goes through the efforts to get to this point.