This is an interesting topic. Being a hearing person though, I will not get into it with too much detail. Instead, I will let you read a blog by one of my favorite authors, Christopher Jon Heuer.
In summary, the crab theory is based on the metaphor of what happens when you put several crabs together in a bucket. The crabs crawl over each other, trying to get out of the bucket, and in the process, none of them escape because they keep pulling each other back down.
This is something that many communities struggle with, including the Deaf community. For a long time, Deafpeople have provided each other with a network of support and mutual understanding and commitment. They still do. However, back when it was more difficult for Deaf people to become successful due to discrimination, an invisible standard–a status quo–was established. Anyone who then stepped outside of the status quo immediately became a product of “the crab theory.”
So, for example, if someone decided that they wanted to work somewhere other than in printing or for the post office, they were then labeled “HEARING-MINDED.” HEARING-MINDED is a sign that means “think like a person who is not like us.” That is how the crab theory goes.
So, with this in mind, read Heuer’s blog here to get a better idea of what the crab theory is and how we can overcome it: http://www.deafdc.com/blog/chris-heuer/2007-05-09/overcoming-crab-theory/ (just as a heads up for those of you who are more literally-minded, he is not being serious when he is giving these tips. These “maneuvers” are generalizations made about the Deaf community that are meant to be funny). Enjoy!