Do you need a counselor for merit badges?

Yes, the Boy Scouts of America states:

When a Scout has an interest in earning a particular merit badge, he obtains his Scoutmaster's/Varsity Scout Coach's approval and identifies another Scout with similar interests to become his partner. They are then directed to the appropriate merit badge counselor. The counselor reviews the badge requirements with the young men and decides with them what projects should be undertaken and when they should be completed. After the counselor has certified that the Scouts have qualified for the merit badge, it is presented to them at a troop/team meeting and can be applied toward rank advancement.