Being a free thinker and announcing such thoughts loudly can be seen as a challenge and threat to other people's belief systems.
Maybe tone it down a couple of notches when talking to them and just be content to chill with them, without trying to assert your beliefs so much (maybe they think you're trying to impose your beliefs on them if you continually go off on tirades).
When the topic comes up, you can still state your beliefs, but do it calmly and maybe even quietly, stick to the general tone and spirit of the conversation, and don't get worked up. If they disagree, then listen to their side of the argument. I think it's just mainly the tirade part that's getting you these funny reactions.