The insulting bit comes when people with an insufficient understanding of the problem come in and offer "solutions" that anyone could have dreamed up in 5 minut

The insulting bit comes when people with an insufficient understanding of the problem come in and offer "solutions" that anyone could have dreamed up in 5 minutes, thereby implying that the new person either thinks the group with the problem is stupid for not coming up with such an obvious solution themselves. It's often the grown-up equivalent of a child learning about a longstanding religious conflict and offering "why don't they just all be friends instead" as a solution.