I deal with incompetence on a daily basis. Everyone from banks to airlines have incompetent employees, and we're not demanding that all customer support agents undergo licensing requirements. We live in a free market and the best way to deal with incompetence is the market. (Ex. I switched my bank after getting frustrated with incompetent tellers.)
Once again: the worst that an insurance salesperson can do is sell you bad insurance. They're not actually involved in medical procedures, so any harm they can do is financial. And if that harm is due to fraud (misrepresenting a product to you), you have legal remedies. Bank customer support people have just as much potential to cause financial harm, but we don't require them to be licensed.
Even more to the point: I can personally sign up for insurance directly on the internet, without talking to any licensed salesperson. If licenses salespeople are so essential to insurance, why can I buy insurance without interacting with one?
As far as I'm concerned, the only professions which should require government licensing are those where tort is insufficient to correct wrongs. (ie. someone can die: doctors, civil engineers, etc.)