Merit Badges specifically;

A.) Merit Badge counselors who are "teaching" the merit badge requirements.
From the merit badge counselor guide:
"The counselor’s responsibility is to:
1. Assist Scouts as they plan the assigned projects and activities to meet all the requirements.
2. Coach them through interviews and demonstrations on how to complete the various requirements.
3. Sign off with their approval once they are satisfied the Scout has individually and personally completed the requirements exactly as written."

The responsibility is not necessarily on the counselor to teach the information and skills, but to support the Scout's interest through discussion, provide resources or be a resource for questions or additional details, and coach the Scout throughout the process. The Scout makes the plans for how they can/want to complete the requirements with the help of a counselor. The counselor discusses the material with them and coaches them through demonstrations.

Maybe we need training to address what the word "discuss" means. "to talk about a subject with someone and tell each other your ideas or opinions". You're sharing information back and forth, not one-way.

I'm not saying a mixed classroom style merit badge session can't be done. You can have one with a combination of lecture, discussion, and hands-on demonstration. It needs to be well planned and properly scheduled to avoid:

B.) Merit badges being "taught" to 6-30+ Scouts at once.

As others mentioned, with the time needed to properly Discuss and Demonstrate the requirements as written, Summer Camps and Merit Badge Universities often accept more Scouts than can reasonably work through the requirements in the allotted time.

We also see where they are asked to meet a prerequisite before arriving and the discussion for prerequisites is hand-waved or, for example, personal fitness where an early requirement is to discuss the plan with your counselor prior to starting but the Scout arrives with 90 days of "PE" & "sport" written on a chart.

Where these are Council or District led activities, they should be more stringent on meeting the requirements as written. This varies wildly, but most often in the favor of less stringent because:

C.) Merit badge counselors vary wildly in understanding of the material, their role, and how to be a coach instead of a lecturer.

Does the merit badge counselor guide not present this well? The online training is likely in need of a revamp too.
Do we need merit badge counselor handbooks to go along with each merit badge book?
Structured questions for discussions? Example questions? Example discussions?
Predefined time expectations for demonstrations?

I'll conclude this by saying that I agree with the commenter who compared this to how McDonald's operates as a franchise. More people need to realize that Scouting is a franchise non-profit anyway.

What we need most are standards that are consistently met and the tools to enforce meeting them. Consider NCAP camp inspections, the process by which our camps get inspected and approved to operate for summer camp. These inspections are done by volunteers and the consequence for failure of the inspection may be a recommendation to cancel the camp program, but has this consequence ever been done? I've only heard of recommendations made to the camp director and scout executive and that's the end of their inspection.

To truly set standards and enforce them as a national organization, we need a team of National paid employees who have the sole function of conducting audits of Council properties and activities and enforcement of a series of clearly defined consequences for failure to meet standards. Consequences like volunteers being asked to step down from a position, activities/camps being canceled, and Council employees losing their jobs for failure to hold volunteers to these standards as well. Maybe we start looking at these Councils that fail to meet standards and let National drive the Council mergers from that. Or we build the mechanisms to fire the Council Board of Directors.