Wait a second, let me get on my soapbox and preach the good word of education for the stage manager.
Yes, yes, stage management is something that is best learned by doing, but what do you think you are doing in grad school? Um, stage managing that's what. Plus, lots of time to discuss your work, be surrounded by like minded stage managers, working on shows much larger then you would be out in the real world, in a safe environment. It also gave me some specializations in dance that I would not have had in the real world - no one would have hired me for the scope of dance productions I was assigned. And, I was working with a support staff of a major regional theatre. Again, before grad school, working small, non-equity gigs - grad school huge shows. But like any grad school, you only improve what goes in, and how much improvement is based on how much work you put in. Many people can be a B- stage manager, go to grad school, and come out a B+ stage manager - which may be good enough.
As far as being arrogant and lazy . . . hmm, maybe arrogant, but working 80 hours a week, 52 weeks a year would not peg me as lazy.
Having the MFA is just one more guarantee that I know what I am doing. When people look at a resume, they are looking for some sort of guarantee that you are going to be a success at their theatre. Trust me, I am pouring over resumes right now looking for one to pop out and scream, I AM RIGHT FOR YOU. Things I look for - 1) SM experience at a major, top tier regional theatre, 2) The fact you have been hired at the same place more then once, 3) proven track record of working in an established producing organization (as opposed to just being a freelancing swooping in), 4) worked with people I know, 5)formal training.
There are a lot of people who don't put an emphasis on the formal training, but I do - because I know what I got out of my formal education. BUT, it's not a make or break point; it's just one more thing that can help me like I know this person will do a good job.
There are a lot of people who do do this job, starting off as an intern, moving up to ASM, and then finally to SM . . . but I think a MFA level can help make you a strong SM, and help you move up faster.
Finally, a grad school education may not help you get jobs, but may help you deal with the jobs you get better.