The "boomerang" phenomenon of adult children returning home is challenging for everyone. As Christians who are reminded in the Bible both to honor our fathers and mothers, and that fathers should not exasperate their children, we would hope that "one big happy family" would result. But as you point out, that's not necessarily the case.
My first thought is that in this situation, where your parents are kindly allowing you to stay in their house instead of you having to support yourself or be homeless, the responsibility rests primarily on you. If you disagree with them regarding politics, theology, or other issues, and you want to continue living there, I suggest that you find other friends to help flesh out your thoughts, and listen respectfully to your parents' ideas without engaging if this usually leads to conflict.
My second thought —and although this may not be an issue for you, it is a major issue for most young adults moving back home — is that the daughter or son needs to have realistic expectations for their level of independence as long as they continue living with their parents. The more independently they act — paying rent, paying for food, cooking, cleaning, doing their own laundry, helping out with chores or transportation — the more they can hope to earn their parents' trust in seeing their child as older and not needing their supervision or discipline. What doesn't work well is expecting all the benefits of living at home — expecting free room and board, Internet, cleaning, laundry, parents paying for travel, entertainment, eating out, etc. — and yet expecting to be treated like the working adult they are.
Ideally, this should be a very temporary arrangement. Perhaps you can share an apartment with some roommates, or your "real job" will come through and you will earn enough to live alone. But if it looks like you'll be living with them for a year or more, then I would suggest sitting down with your parents and asking how they would like to handle talking about issues when you have different opinions. Would they like to have an open dialogue and learn what you think, or will that just be frustrating or disheartening to them? Don't assume that just because you are all Christians, they want to have the open dialogue that you would like and that you experienced in college or graduate school. Many Christians are not at all interested in dialogue (unfortunately) and would rather dogmatically lecture than seek to understand someone else's point of view. The only way to know for sure with your parents is to ask, and then to respect their wishes when you're in their house!
I’d also suggest that you negotiate a contract with them, which includes how long you agree that you can live there, and what your financial and other responsibilities will be while you live there. I would suggest six or twelve month increments, like a lease, at which point either of you can change or terminate the arrangement. They may be concerned about how long this could go on, and you may be reducing their independence as well. Taking the initiative to discuss this should help them see that you are committed to moving out as soon as you are able, and that you are an adult who is responsible and hardworking.
I wish you the best!