I used to deal with people arguing with me about me being a vegetarian. They ask questions like "Is it because you are from India?" and "What is wrong with you?" and "That is so stupid". I had my reasons. I had my justification for choosing to not eat meat. When I try to explain myself, they try to "convince me" otherwise.
I learned, the hard way, that they are not trying to insult you. But just trying to "help" you. When you believe in something that people don't generally believe in, they think you just don't know any better. Some people are genuinely just trying to learn the root of your belief system and understand better why you do it a certain way, while some just think all you need is some talking to.
This is what I started telling people:
Oh it's OK, I am not in a dilemma. That is just who I am and I know why. I have my reasons and I wish to stick with it.
People usually go "Ooookkk..." But then again, it is in fact your belief system that isn't up for debate. Just be direct with them.
Important things to remember when trying to not engage in an argument or debate:
- DO NOT try to convince them that your way is better than theirs. You don't want to seem like you're preaching your belief. When someone even thinks about talking to you about this, they are coming from the other side. It is just as annoying to them as it is to you if you try to convince them otherwise.
- Your question says "Religious or cultural". This shows a very good attitude about this whole thing. As in, you don't even want to dig as deep as "Why". Keep it that way. DO NOT mention either of those terms. That is just opening up a can of worms and leads to more questions/accusations/debates.
- Sound confident in what you say. Simply state a direct statement that tells them to stop "trying" to talk you out of your belief.
- Maybe start talking about something else right after. You want them to know how disinterested/indifferent you are towards their opinions on your beliefs. Just state the statement and carry on with something like: "But anyways, how was your day today?" or something, depending on the situation and the person you are talking to.
In conclusion, try to be as clear as and as direct as possible about your confidence in your belief and they usually stop. I've been there and I know it can get annoying.
P.S.: Keep in mind this: IF someone is asking you questions regarding your belief system with genuine curiosity and willingness to learn the reasons, you should definitely tell them why. Always support others willingness to learn. When they utter words like "But what about...." is when they are trying to convince you otherwise and when you need to stop the conversation. Don't immediately throw this at people because you make a lot of enemies doing so. Entertain the talk, block the debate.