Because the promise of the MBA program was that you could be air-dropped into an industry that you had zero experience in, and your MBA education would automatically make you the smartest in the room. You (supposedly) didn't need that industry experience, applying MBA principles would be enough. And it destroyed enough companies that they developed a not-undeserved reputation.

Now, if you already had relevant experience, then went and took the MBA course, and were able to identify when to lean on which, great! But, of course, part of that education is telling you that you don't NEED that experience in the first place, and if it and MBA principles disagreed, you should rely on the MBA principles.

So, if you took the course truly to heart, then, well, yes, you would be somewhat "dumber", so long as you define that as "unable to make correct decisions."

Having been a software engineer and gone on to do a MBA, none of what was taught for the degree reflected the attitude that you're describing. At no time did anyone tell us to ignore our prior experience - rather we were told that that our prior experience plus a business education would be valuable to future employers (which it is).

There was no expectation of being "air dropped" into an industry, and in fact, industry recruiters looked for candidates who already had prior experience when picking students for interviews and hiring. The students who had no relevant experience for the industry they were recruiting for (e.g. ex-Peace Corps or mgmt consultant looking to transition to tech or industry in general) were the ones who struggled to find roles. Your assumptions about what an MBA education entails are incredibly far off the mark.

I have an MBA and a CS degree so responses like this make me chuckle. I generally don't bother to engage with those with an MBA-phobia who haven't done it themselves.