Being a professional is more about how you conduct yourself than the exact way you take a photo.
My pro manual argument for myself is that it's actually one more variable to deal with in terms of getting the images to look exactly how I want.
ISO/Aperture/Shutter Speed
OR (using A-mode as the example) - ISO/Aperture/Exposure Compensation/Metering mode.
And if I make a mistake in manual, it's my fault and I can learn from it. If the camera guesses the scene wrong, it will never learn.
I think there are a lot of people that learn about editing style or shooting formats, rather than content (subject, emotion, moment, composition, lighting and other in-camera techniques, etc).
And if those fundamentals are weak, it can feel like putting a coat of paint on a crumbling structure. The paint is great if there's a strong foundation, but without it...