There was a point in my life where my main focus was playing in a band a pursuing the life of a musician. To be a better (for lack of a better term) “rock star” you can’t really do anything else besides take music lessons and practice your instrument. Acting is the same way in the sense that you can practice your craft by performing and auditioning, but there are many more options available for acting education than there are Rock n Roll Schools. Yet you never hear anyone rail on a rock star because they didn’t go to Berklee.
So an education in your craft is necessary but how much is really the question. Going into an MFA program is usually dependent on whether or not you feel like you can learn more in an educational setting. Some people like that academic setting where most of their focus will be spent within a certain program while others can achieve the same knowledge by attending a class once a week hosted by a theater company.
The question you asked kind of steered towards the equation of “no MFA = non-theatre career.” I don’t think that’s exactly what you meant nor do I think that is true. Out of all of the actors I know, only a handful have MFA degrees, and many of them I think are extremely talented. I myself have a degree in English instead of Theatre&Drama, although I was accepted into the Acting Specialist program and participated while at school. Is my knowledge as vast or in depth as others? Probably not, but that doesn’t mean that I don’t produce quality work (at least I’d like to think so).
Overall, I think skipping or doing an MFA is completely up to the individual, their desire for knowledge and the way they learn. Money shouldn’t be an issue if an MFA is really what you want to do. You can always get a student loan and some programs will even pay you while you’re there since you TA while in the program. MFA or not, there will always be people who will have the passion and drive to produce quality work in whatever medium they choose.