Some do marry outside their religion, but they are disobeying the Filthful and Disgraceful Slavebugger in the process. Usually, it will result in the person being marked as "bad association".
About the only way out of this is you will have to study and become a witless yourself. Yes, the study will be handed to a "brother". Yes, you will be expected to do everything they want you to--throw away your Christmas and church items, quit smoking and gambling, give up your horoscopes, and the like. Then you will have to go out in field circus, regularly. You will then need to be baptized.
Even then, there is no guarantee. They are programmed not to marry someone "too soon out of the pool", and they are not distinct as to what constitutes "too soon". Usually, this is a means to allow someone else to take them out from under your feet, and the hounders can bumble this as long as they damn well feel like it. Then, you have all those stupid rules about dating--there always has to be someone watching you at each and every date. Even after you are married, you still have those stupid rules--which the hounders will do their best to make sure you are abiding by (and if she is strong in the cancer, she will not break them anyways).
Once you are in, the hounders may in fact decide to prevent you from having her after all that work. If they see "Value Destroyer Training School" on you, forget it--they are going to do all they can to prevent anything from happening. It will never be "long enough" out of the pool. Or, they might slander you to make you look like s*** to her. They might even play down your hours in field circus and play up whatever you are doing wrong (and there is always something). All this has nothing to do with physical attraction or lack thereof--those witlesses are programmed to believe that worldly people are so much urine or poison, and walking corpses.
Beyond that, there are always issues with what the religion does to people. Extreme behavior aside, these people always think of the next boasting session, field circus, and that next call. Any children will have to be raised as witlesses--meaning no fun while in school, no good jobs, and the children have a better than even chance of spending the better part of their adult lives still with their parents. Those children will have to stay up past 10 PM on school nights (usually the most popular one for unit tests the next day). You will have to take them to the boasting sessions, and then keep them silent for two hours or more at a time.
Make no mistake--if you marry a witless, you are in for a lot of huge headaches.